This is an awesome question. The answer depends on which point of view to take.
Developer
If you work at your job on the open-source
it means that your contributions will be visible better than any CV would be able to tell.
It means that you don't have to leave your beloved project behind when you switch jobs
it means it won't die if the company decides to discontinue to work on it
Open-source is great because you can use it for free (most of the time)
which means you don't need management approval to use it at work
which means that you can learn it online for free (compared to proprietary software and PaaS)
You can read source code and learn from the author - see real-life code, not educational examples.
Company
Open-source is great because it is free (most of the time). Sometimes it may cost to pay developers to support solution based on open-source, but I would say in general it is economically good anyway.
Open-source can be a safe bet because when you use propriety soft, you depend on other company
which can stop supporting product
can be slow on delivering new features, bugfixes
can be forced to stop working with you because of law (for example, US sanctions)
With open-source on the other hand, you are safe, because if you really depend on some soft you can fork it and use it.
You can sell open-source as PaaS, which will give you immediate profit almost without any effort. This is what AWS doing for hosted MySQL, Redis, PostgreSQL, etc.
If a company produces open-source it is more attractive for developers, because they will have a chance to work with open-source.
Open-sourcing something may give you free testers and sometimes free labor. Some companies use open-source as a hiring process, instead of the home task they ask to contribute to their open-source projects.
Humanity
Open-source has a great impact on economics. Open-source and free software enabled a lot of growth, a lot of IT business exist because there exists an open-source solution, they wouldn't be able to sustain without it. For example, Linux and nginx which serving 80% of whole internet traffic. Git is the part of Github success. Etc.
Open-source enables scientific research. No need to pay for soft makes research cheaper.
Companies have no need to produce the same propriety product, no need to waste time and resource. Instead, they can work one product - big corporations contribute to Linux and other big open-source. Imagine that instead, each company would support its own crappy OS.
Maintainers
The most interesting bit. Often maintainers get nothing for their work (unless this is their day job).
There are very famous open-source maintainers, for example, Linus Torvalds, Yukihiro Matsumoto, etc., which get a lot of fame praise (probably a bit more money, because of status), but most of the open-source maintainers get nothing. No fame. No money.
There is a strange idea that open-source will make you famous or respectable. It can happen, but only if you make a very popular project.
There is a long-standing problem of how to make open-source sustainable, for example, we should make special licenses which will force big companies donate-back.
Or maybe we can pay open-source maintainers from tax money, and add tax for tech companies (the same way as we pay for roads - if you have a car, you should pay road tax).
There is this donate button on the Github, but I don't think of it as a solution. If you are a social person, you can get money with it, but otherwise...
PS
I have so many ideas on the subject, maybe miss something
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This is an awesome question. The answer depends on which point of view to take.
Developer
If you work at your job on the open-source
Open-source is great because you can use it for free (most of the time)
You can read source code and learn from the author - see real-life code, not educational examples.
Company
Open-source is great because it is free (most of the time). Sometimes it may cost to pay developers to support solution based on open-source, but I would say in general it is economically good anyway.
Open-source can be a safe bet because when you use propriety soft, you depend on other company
With open-source on the other hand, you are safe, because if you really depend on some soft you can fork it and use it.
You can sell open-source as PaaS, which will give you immediate profit almost without any effort. This is what AWS doing for hosted MySQL, Redis, PostgreSQL, etc.
If a company produces open-source it is more attractive for developers, because they will have a chance to work with open-source.
Open-sourcing something may give you free testers and sometimes free labor. Some companies use open-source as a hiring process, instead of the home task they ask to contribute to their open-source projects.
Humanity
Open-source has a great impact on economics. Open-source and free software enabled a lot of growth, a lot of IT business exist because there exists an open-source solution, they wouldn't be able to sustain without it. For example, Linux and nginx which serving 80% of whole internet traffic. Git is the part of Github success. Etc.
Open-source enables scientific research. No need to pay for soft makes research cheaper.
Companies have no need to produce the same propriety product, no need to waste time and resource. Instead, they can work one product - big corporations contribute to Linux and other big open-source. Imagine that instead, each company would support its own crappy OS.
Maintainers
The most interesting bit. Often maintainers get nothing for their work (unless this is their day job).
There are very famous open-source maintainers, for example, Linus Torvalds, Yukihiro Matsumoto, etc., which get a lot of fame praise (probably a bit more money, because of status), but most of the open-source maintainers get nothing. No fame. No money.
There is a strange idea that open-source will make you famous or respectable. It can happen, but only if you make a very popular project.
There is a long-standing problem of how to make open-source sustainable, for example, we should make special licenses which will force big companies donate-back.
Or maybe we can pay open-source maintainers from tax money, and add tax for tech companies (the same way as we pay for roads - if you have a car, you should pay road tax).
There is this donate button on the Github, but I don't think of it as a solution. If you are a social person, you can get money with it, but otherwise...
PS
I have so many ideas on the subject, maybe miss something