Yes, there are several websites that respect it (Netflix, Roku, Verizon to name a few). And the number is growing now that GPC is mandated by California & Texas state law in the US, I am not familiar with GDPR's stance on it.
Users absolutely still need to block trackers but GPC tells companies to not share your data that they collect themselves, which obviously cannot be blocked by an ad blocker otherwise you wouldn't be able to use the service itself.