Curfews are for children and teens. If you are relying on EA for story progression, then there aren't any controls. I don't recall the curfew system breaking down for me under EA standard, but it wouldn't surprise me if it does.
If you are using NRaas mods, the controls for curfews are part of StoryProgression. We can also restrict certain lots from allowing SP to push sims to them by age group, so children shouldn't be showing up at more adult open late venues like bars and dance clubs for example. I believe that AwesomeMod has its own way of handling these things. I have to wonder if some of these things are world-specific as I don't have my SP curfews set very strictly and I never see children out and about in the middle of the night as others sometimes report. For teens it will depend on their traits.
YAs and older will be pushed out to enjoy things in the town also as per their traits and whatever it is your sims are doing at the time to make the town feel busy. Their resulting energy drains should really only be temporary, the game itself is supposed to take care of sims' basic needs for them when they are off-screen. But NRaas SP also has settings that control after-work (thus after-hours) pushes on the inactives. If you are using additional mods like More Sims in Clubs and Townies Out on the Town to name a couple of famous ones, of course those will also have an impact.
Note that if you happen to be playing Uni World, then all bets are off. There is very little logic to what sims do with their autonomy in that world.