Honestly, there's no good reason at all. I'm just so used to resizing my web browser with the mouse all the time to read things better. I should probably break that habit.

I do occasionally get weirdness with tiling Chrome (though I still do it), when websites try to resize their windows and my window manager won't let it. Some crazy websites depend on multiple sized/moved windows as well, e.g. this thing won't work unless I float the browser: http://news.ycombinator.com/item?id=1646430