I used to not see point in rgb but if you have a glass side on your case, you might as well have some lighting in there or its just a dark void.
I just realised that only three parts in my case don't have rgb now. Power Supply (which I can't see anyway), chassis fans (which are mostly hidden), and storage drives (which are either under a heatsink or hidden).
It wasn't intentional... okay, some of it was... I could have chosen an AIO with non rgb fans but I like being able to see the front of case. GPU helps brighten up the bottom area of PC.
Prior to current PC I only had it on Keyboard (as it helped read keys) and mouse. Now only thing that doesn't have (unessential) RGB on it is my monitor. Its hardly a reason to pick a particular monitor though.