I used to use walkthroughs all the time for everything on every playthrough, but now I'm too lazy, so I don't typically use them that often. Only if I get stuck and don't know what to do. Or there's some boss I can't beat. And if I feel like completing extra sidequesty stuff.

Although I will always use one for FFX-2, because getting 100% requires an insane amount of attention to detail.

As for official guides, I only have the one for FFIX which kind of sucks due to that defunct online thingy majigger being referenced on every page.