Here is a question that would seem to have a lot of opinions for answers. Are questions like this ok?
It's asking about what commands is ex mode are actually useful.
A "what commands are useful"-question is a very opinion-based question. Some might consider command 'foo' to be very useful, but the next might consider it to be stupid.
This would quickly spark a discussion. While this discussion might be interesting, it's not a good fit for the SE format in general. I don't see why vi.SE should be an exception.
However, the question you link to, doesn't ask "what commands are useful", as I read it, it asks "What is Ex mode, and how is it useful?". This is a different sort of question that can be answered objectively.