I loved this from other sites because it helps keep things clean and concise in the profile. For example, I'd like to use it to tag several writing examples of mine since I usually do multi paragraph posts. That would be quite the wall of text, but having something like a collapse would allow things to be neater since you can open and close the examples. I don't know if this is a feature but I couldn't seem to get it to work.
I'd also use this for plot ideas in my profile since ads don't give a lot of space for more fleshed out or complex ideas, so I'd rather just collapse the more complex ideas in my profile and have my ads reference them a little so it can be pointed that there's more if someone is interested.
Let's be honest, if someone sees a wall of text in your profile they are going to be intimidated and not care to read it all, but collapses give them a bit of space to see what's there and choose what they want to read up on about your character or ideas.
This is unless there are ways to do it in an ad that I haven't seen, but so far all I've seen is a very limited text limit for them which doesn't give a lot of room to expand upon your idea further. I feel if someone can see that idea for all that it is it would give them a better idea of it it interests them or not.
tl;dr, Please let us have Collapses or Spoiler Tags in profiles so we can make our profiles less intimidating by giving the choice of whether someone wants to read certain things so they easily skip to what is most important to them to see rather than skimming a giant wall of text. :)