Well, i personally root all my devices. It gives me a lot of benefits: easy backup/restore of entire ROM or just user apps and their data (or both, what i actually do on regular basis), changing ROMs at will, changing kernels and applying tweaks, customization of ROM itself with mods, getting rid of bloatware to free more RAM and extend battery life, stopping ads everywhere etc. I personally like it very much because it's my device and i want it to do what i say because i said so, period.
You don't have to install CM, but you can if you want. I didn't tried it yet on S4 because i'm happy with stock and too lazy to start from scratch again with new ROM. But i used CM for a long time on S2 and liked it very much.
Best method for rooting i9505 (IMHO) is with CF-Auto-root: . Just read the OP carefully and follow the steps. There are other methods like flashing pre-rooted firmware, but i never tried it myself.
Hope i answered your questions.
Thanks for the response, I will probably root it simply to get rid of some of the bloatware etc. I'll see how I get on, probably gonna have questions on what to do with a rooted device and how to do certain things but i'll find out along the way.