As everyone said already, they absolutely matter to the seller, and they help other buyers making decisions (imagine you only ever saw “good job” or “fast delivery” on every seller’s gigs), so they matter doubly.
I´d say maybe even triply, as a seller who feels their work is appreciated may feel inclined to favour an appreciative buyer’s inquiries over such of an unappreciative one (as we all know, some even leave no review at all even if we know they got just the same great quality job as a buyer who does) in case they can´t accept both requests. So, they potentially matter to seller, other buyers and buyer who leaves them - 3-in-1!
It may be time-consuming though, for people who order much, and I don´t have any bad feelings towards buyers who I know do and I wouldn´t expect elaborate and long reviews every time either, but I appreciate it a lot if the review isn´t exactly the same every time. There´s only so much a seller can say in their thank you for the review text too, but I take a bit of time for that as well, and not just copy-paste some text or write the exact same every time.
A short text totally works, though, and “good job” or “fast delivery” is much better than no review too, after all.