system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek]Why don't vessels travel at maximum warp all the time and do they have or need any protection when they travel at warp speeds?

It was probably asked before but I think we need a break from Star Wars questions as they seem to make out 90% of this sub now.

So I started watching ST:TNG again because I haven't seen it since I was a kid and every time they need to go from point A to point B it's at different warp speeds.

Now I know it might be because they have time and the crew needs to rest but is there any other reason to do so? Energy preservation, strain on the ship or the warp core maybe?

Also, do they have any radiation protection like Serenity has and is it possible that something from Event Horizon or Warhammer 40k might happen while they travel at those speeds?
gpt
Higher Warp levels put more strain on the drive systems in addition to using up more anti-matter (fuel). 

Spoilers for an episode of TNG:  As we see (you'll see) in TNG, some areas of space can actually be damaged by frequent high warp field levels as well.