There’s a lot of merit to taking a week or two beyond the standard. 2 weeks isn‘t a lot of time to hand off all your work, go through the usual HR bureaucracy, and make sure you have contact info for anyone you might want to stay in touch with after leaving.

If it’s an amicable departure 3-4 weeks can be a lot less stressful for everyone.

6-8 weeks is kinda weird though, unless you‘re extremely senior and on critical path for a lot of things, or you‘re using up accrued PTO.