I don't use an exclusive tiling WM, but prefer a hybrid stacked/tiled approach.

So my argument for the stacked approach (or why I prefer floating windows sometimes) is because sometimes, some of my windows don't really work well as a small tiled space - remote desktop windows for instance. Or sometimes, there's too much white space in a window and resizing it into a tile may make it look weird, like a web page (especially web apps). So tiling doesn't always work for me, so for the most part I prefer floating/stacked windows.

As for tiling, it's great when you've got multiple things you need to refer to, or keep an eye out on. For instance, in my typical tiled work setup, I would have one tile for emails, one for chat, one for my browser, and one is a terminal or IDE. The terminal or IDE would be my main work area, I need the browser open at the same time to look at help or other reference material and maybe copy-paste code, and the emails and chat I need them open to keep an eye on things. I might make use of other monitors or workspaces for other things, like full-screen windows such as remote desktop sessions, or other monitoring stuff.

So for me, both floating and tiling windows are useful, so I prefer a general stacked WM that can also do tiling.