It depends on how much "down-time" your characters engage in - most often this occurs when PCs want to craft magic items, do research, etc.
In some character-driven campaigns, particularly political ones, the passage of time becomes important when it comes to other factions pursuing and accomplishing their goals.
Often, after completing an adventure or story-arc, I will ask the players what their characters want to do next. Then, if they don't have any immediate goals that they want to pursue, I'll advance the timeline a couple of months until their next "adventuring opportunity" comes along. Something about PCs just running from adventure to adventure without ever sitting down for some R&R just rubs me the wrng way.