I know some people aim to have a 'spooky' session around Halloween, or a holiday session around the holidays. Other people have worlds with holidays of their own which can and do come up. And other times the game world has no real holidays that come up, or references to real holidays. None of which is wrong. The question is though, given the choice, which of the three would you prefer?
When I can do it, I like to take influence from the time of year for certain sessions. Having ghosts and a horror/mystery around Halloween, or finding a reason to have a session around a large gathering for Thanksgiving can be a lot of fun. It also lets you tap into energy already going on around the players.
Sometimes that doesn't work. And sometimes people have bad relationships with a holiday so it is better to avoid it. Still, when able, I find it adds a fun extra layer to the game.
How about you?