I began to root once I was convinced that it would work for me. My first rooted device was the LG Optimus V. I still have it, and it's still on the original battery! That thing could take a beating! I've used at least five different roms on that phone, including squid's KitKat rom. It's now settled back to Mirage's GB rom. I've also rooted two Kyoceras: the Rise and Event. I got the Event to replace the Rise, which I accidentally bricked to boot loop hell. From April of this year, until October, I had a rooted LG Optimus F3. For whatever reason, that one began overheating uncontrollably the last week of October. It slowed down so much that I had to ditch it. The micro SD card was fried, too!
My main reasons for rooting were to increase usable space, and have better control over backing up apps and settings. The only low level settings I ever tweaked were for 3G, wifi, and GPU.
I got my first tablet in August, a Samsung Galaxy Tab 4 7.0. I haven't had to root it as I have more than enough space to install the apps I want, thanks to app2sd coming back on KitKat. I have plenty of games I want to play on it, including Republique (the biggest of my bunch). The interface is a tad slow on that one, but perfectly functional. I also like the battery saving feature... I use that along with Greenify, which used to require root for full functionality. Greenify now runs well enough for me in unrooted mode.
My latest phone is the LG Tribute. It does lack space for bigger apps, but I've been able to fit the ones I actually use at least weekly on that phone. For that one, I've used web links to social sites like facebook, Google+, and twitter on the home screen, instead of installing their apps. I do have a few installed, including facebook messenger and Instagram. This phone actually has a better GPU than my tablet! Not bad for a $80 phone! For that alone I'd love to root it so I can make room to install more powerful games, but I'm happy playing most of those on the bigger tablet screen. I also have Greenify on this phone to help extend the 2100ma battery's life between charges. I could see Lollipop landing on this phone, but that might be more likely with the Tab 4.
So that's it for now... I'd love root for the Tribute, but it's not a high requirement for me anymore. Nice to have devices that run relatively well out of the box! I can at least change the launchers if I wanted to, but the Tribute has the same basic one that the G3 uses, which is great. Someday, if I can afford contract service, I'll probably use nothing but the Nexus devices.