Speak about the whys, not the hows. It's okay to include a few favorite libs and patterns but it should not be the main focus of your comment.
No Googling! I am interested in Your opinion, experience, anecdotes, and gut feelings.
Why is it so popular?
When do you use it? Does it belong to the back-end, the front-end or both? Do you use it together with specific patterns or tech stacks?
Do you use it because it's your stack's best practice? Do you consciously choose a stack the relies on immutable data?
Did you ever have issues with mutable data?
Whatever pops into your mind about Immutable Data.
All comments are welcomed, there is no wrong answer!