I have some pretty good reasons for rooting that are almost never mentioned when people are asked or respond to such comments/threads...
1. I replace the systems hosts file to block porn, spam, tracking, and sites known for redirecting requests (also blocks most web ads, but not in app ads, so devs can still get their money from free with ads apps), this not only speeds up internet based traffic, but also prevents garbage from collecting on your device.
2. I also root specifically for the option to perform backups of the system in case something goes wrong (including full phone backups, device ID backups, and titanium app backups so I can keep my game progress between phones when an online restore is not included by the dev. There is nothing like spending 20-200 hours playing a game on a device over a 2 yr contract then moving to a new phone and having to start over or just stop playing your fav games...)
3. change the boot loader image and startup animation, if for no other reason, in case someone gets a hold of my phone and factory resets it, I can always prove it was mine simply by having them reboot... but also as the stock image and boot animation usually sucks.
4. other reasons that most people perform rooting, trying different roms and kernels and removing bloat (a little different from me though, I remove the default ringtones often leaving only 1 ringtone, 1 notification sound, and 1 alarm, and also I remove the excess fonts I don't need)