I can't speak for others, but here are a couple of the benefits I see.
- Less escaping necessary. q{brace {fun}} does what I want. I can say q{"quote" 'fun'} too. You do need to escape braces in a q{} if they're unbalanced, but otherwise it just works.
- It stands out a little more for small expressions (q{} vs '').
- Even if I don't have to escape anything now, I might have to later. If I code with q{} today, it saves me having to change to it later.
- Likewise, it's easier to go from q{} to qq{} than it is to go from '' to "" if my interpolation behavior needs to change.