I float all my quilts, I think the only one I ever pinned was the very first quilt I did on the LA, and I had so much trouble getting it mounted I never attempted it again. I make a lot of queen and the occasional king quilts, along with smaller ones.
I do pin my sides and I pin when I get to the bottom, I make sure it's staying square with each advance and I do sometimes pin the edge in the middle if I need that to keep it square. That isn't needed very often. I do have a cord mounted along the front that I have slides I can move to line the quilt up vertically as I advance. Don't recall who posted about that, but it's really made things easier for me.
As to quilting space, I ran into that with my 15" Bailey, but it didn't have robotics so wasn't that hard to deal with, and with my 24" HQ Fusion, I've had a few times I'd needed to be careful on large outer corner designs, but for the most part it's not an issue.