Do I have to Re-Root my Android Smartphone After Installing Custom ROM?
The answer is no, most custom ROMs, 99% of them, come with root and a Superuser app like Superuser or SuperSU installed.
Some of newer Jelly Bean ROMs may require you to install root separately but most custom ROMs in general come rooted.
Why would ROM developers want you to root your phone again?
Exactly, sometimes you can use common sense but for those of you who didn’t know, I hope this helps and you can flash all the custom ROMs you want, most of them come with root yes.