I didn't technically "use respite" for my first foster child - we had 5-week vacation planned waaaay in advance of the placement and I was not allowed to take him out of state for that long, so I asked the workers to arrange another placement. But it ended up functioning as respite, because he came back into our house when we returned and stayed until he was placed with kin. I think it actually worked out well - although it would have been a heck of a lot better if they had just let me take him along. His mom was incarcerated, so no visitation to worry about. When my STBAS was placed with us, I was very aggressive right up front about how we were TAKING HIM WITH US ON VACATION and they complied (his mom was also incarcerated). So my advice for people now who are going on vacation is to be a squeaky wheel about how the child deserves not to be left behind and try hard to get authorization for the travel.
For therapeutic-level kids, I think regular respite of some kind is a very good thing for everybody involved, provided that it's not a new provider every time.