Well, mostly if you use tools that have a "view portal" or depend heavily on pop-out style toolboxes. The WM is constantly resizing your windows, which makes it a chore to keep everything adjusted, and pop-out style toolboxes are pretty much best at on-top usage by nature, rather than tiled.
I use CAD software on a regular basis, and while I managed to make a tiling WM work for me for maybe 6 months, returning to a floating WM was a relief. If you work directly with text all day, I bet they are great, but for me...