Daystrom Institute

So, this may be a frequently discussed topic, and I'm sorry if so. But I was watching S1 of SNW and there was a scene where an early "shields up" saved the ship from serious damage. And now that I think of it, I just can't come up with a good reason why shields aren't up all the time, with a few obvious caveats.

1. Yes, shields must be down to transport, this seems like the most obvious reason to have them down. But we see plenty of episodes where shields are brought down momentarily for a transport. Why not do that always?
2. One reason brought up frequently is that raising shields could be taken as an act of aggression. But if you arrive with shields already up, then you're not doing anything aggressive, you just arrived that way, so I don't think this makes much sense in a world where most Starfleet ships just keep their shields up.
3. I don't know for certain, but it seems possible that shields may not be usable at warp. I don't remember any specific episode where that happened, but it seems possible. But even then, a ship could just be programmed to bring them up as it drops out of warp.
4. I guess it could be possible that the power usage of the shields is too much for the day-to-day use. But again, it seems like a lot of missions clearly begin with "dropping out of warp into an unfamiliar area" and those are the times where your shields should just be up by default.

Of course, I know the answer is that "shields up" is great dramatic dialogue, but I guess I wondered if there are any more satisfying answers than that?