I come across people fairly regularly posting on android forums who avoid rooting because they "don't want to mess with custom ROMS". It prompted me to write this post, if for no other reason than to say that...
You can ROOT without installing or running a custom ROM.
I've been unlocked since day one as unlocking fully wipes your device and I didn't want to go through the trouble of setting everything up twice since I knew I'd want to root shortly. I rooted my phone within days of getting it, not to run custom ROMs but to have access to all sorts of Root-only features. Personally, I still run the stock ROM and kernels, but root gives you access to so much more.
Here are just a few reasons I rooted.
1. Wireless tether. I've had wireless tether since my original Droid (albeit a fairly insecure Ad-hoc implementation). Now, there are supposedly some non-root wireless tether apps, but I'll stick to what I know.
2. Titanium backup. If you ever want to change a ROM, TB is priceless for getting your phone back up and running.
3. Custom features - Installing custom boot animations, certain features of apps like Nova launcher, and dozens of other root-only apps make rooting invaluable in my opinion.