I guess most users do, but people who write in outliners need a little more graphic relief because our work is totally text and structure. Adding a bit of graphics is like adding spice to a sauce. And they're fun!
We're lucky because Font Awesome is such a great collection of icons. And it keeps getting better. If you're developing web apps, you're nuts if you aren't using Font Awesome. Seriously.
Anyway, until Fargo 0.65 it was a lot of work to add an icon to an outline. What changed is that we created an icon chooser dialog that makes it easy and fun.
If you're using Fargo, you can try it out with the Icon Chooser command in the Outliner menu.
If you're not using Fargo, here's a little demo app you can try. It doesn't do much but allow you to browse the icons. When you click on one, an alert pops up saying which icon you chose.
If you're a programmer, the code is free to use under the GPL. That means any improvements you make must also be licensed under the GPL. And it would be nice if you said where you got it. :-)