system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] Warp drive is down for maintenance, we are proceeding on impulse power. Why would they do that?

I believe this happens pretty commonly, but I just saw at least one explicit instance in S1:E22 of TNG, where the warp drive is down in deep space for some non-emergency reason, but they're continuing on course under impulse.  

Why would they waste the fuel?  Impulse isn't going to get them anywhere significant.  Why not just hold station while the main drive is down?
gpt
I mean, there's no need to keep burning fuel if the engines accelerate them to .25c. They get to that velocity and then proceed forever at "impulse speed" until they fire engines again to change their course. And/or go back to warp speed. 

Space has no (measurable) friction pushing back against the ship once it starts going in a direction. So the impulse engines just need to push once, or at least long enough to safely accelerate, before being shut down. 

And while the distance covered at impulse is negligible compared to warp, it's still progress toward their destination. It's a pain in the ass to come to a "complete stop" in deep space, given that everything is moving and so you're technically always moving relative to other points of reference.