There's an issue in tiling window managers, that I think a lot folks who are used to floating window managers never expect. I wrote a post to the Awesome listserv a while back explaining this to someone, and it seems to have struck a chord (I saw the post linked to last week). I thought I'd write a brief post here to explain what's going on in a more clear and general way.
When tiled, windows don't seem to take up all the space that's available to them. This creates weird "gaps" between windows. But only some windows: Firefox is immune to this problem, while terminal emulators like xterm, and urxvt, and gVim, and emacs get all funky.
The application that are affected by this draw their windows based upon a number of fixed width columns. We'll note that terminal emulators, as well as GUI versions of programmer's text editors like vim and emacs, all used fixed-width fonts and often allow you to set window sizes based on the number of columns (of characters).
As a result, these applications are only able to use space on the screen in increments of full characters. Most of the time, in floating window managers, we never really notice this limitation.
In tiling window managers you do notice, because the window manager forces the windows to use all available space, except in some windows it leaves these weird gaps at the bottom and right of the window. Sometimes the gaps end up in the window, as unusable buffers, and sometimes they end up between windows. It looks funny, pretty much no matter how you slice it.
What You Can Do About It
The truth? Not much.
The Awesome Window Manager, by default shows the gaps between the windows. I always found this to be the "more ugly" option. You can alter this behavior by searching your configuration file for size_hints_honor and making the line look like this:
c.size_hints_honor = false
This tells Awesome to ignore windows (client's) when they say "I want to have these dimensions." It doesn't fix the problem but it does get rid of the gaps.
The real solution is to tweak text sizes, fonts, and any buffering elements (like a status bar, mode line, or widget box), and window borders so that the windows aren't left with extra space that they don't know how to cope with.
By real solution, I really mean "only option:" it's really impossible to get all of your fixed width applications to have exactly the right number of pixels. You can get close in a lot of situations, and I've always found this to be much less annoying than using floating window managers.
The Original Post
Just for giggles, I've included a quoted portion of what I posted original to the listserv on the topic.
The one big of information that might be important: The urxvt terminal emulator, when not "honoring size hints," is unable to really properly draw the "extra space" with the proper background. I suspect this is a bug with the pseudo-transparency system they use. As a result there are often a few pixels with the background in an inverted color scheme. Same problem as above, but it looks funny if you're not used to it.
What's happening is that urxvt (like many terminal emulators) can only draw windows of some specific sizes based on the size of the characters (eg. x number of rows, and y number of columns.) So while you may have larger and the equivalent of say 80.4x20.1, urxvt can't do anything with this extra space.
If you honor size hints, the windows will end wherever they can, and use as much space as they can, but leave gaps between windows if the total space isn't properly divisible. If you don't honor size hints, the windows themselves take up the extra room (but they can't do anything with the extra room, so they just leave it blank, and sometimes the transparency is a bit wonky in those "buffers").
So there you have it. I hope this helps!