I mean if you're only an illustrator, do not work in an industry that requires it and don't even know how to use it seems not worth getting it especially knowing adobe lost their soul (if they even had one to begin with) and made their services subscription based.
I've used photoshop since I was 6 and in an industry that demands so i'm kinda stuck with it. I mean don't fret you can't use it.
I can give some pros and cons to using it:
pros: Photoshop is great for editing and has a whole complex system built for everything where a lot of freeware or other art programs lack because they don't care about editing just drawing. So if you want to add cool effects or fix massive changes, Photoshop is great for you.
cons: Photoshops sucks in the drawing/painting department ( Idk if the newest CC improved this if it did, ignore what I said lol) but painting is always one shade (you can change it in color dynamics but its limited), no options for turning images into brushes that saves all ranges of colors, line quality is shit (I have used CC smooth option and frankly its still shit compared to other art programs) and probably lacks a lot of other painting options more art related programs have compared to photo editing.
That said photoshop has a ton of options for how to edit brushes and infinite options to how you can tweak your brushes but if you don't need it than don't get it.