system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] why do they travel so slow sometimes?

What is the benefit of going warp 2 or 3 at times? Why not a more "normal" cruising speed like warp 7? Are they conserving fuel or what?
gpt
Not so much conserving fuel as cutting down on maintenance time.  [non canon opinion].  A pal once told me if he rode his bike to work everyday he'd have to do a half hour of maintenance on the week end.  If he took that same bike out on Saturday afternoon and rode the hell out of it for an hour he'd have to do two hours maintenance Sunday afternoon.

Going at Warp 4 and above means repalcing dilithium crystals etc sooner.

Also, some missions might require more prep time then others.  If you are going to be near the Neutral Zone with a chance of combat, you might want to give the crew a few extra days of training.