I think the real question you're trying to ask here is: How can I avoid letting my players take free long rests whenever they want?
In the situation you described, your group felt free to use lots of resources on a minor battle, because they knew they could just rest right afterward.
There are two approaches I use to avoid this. One approach is time pressure: if the group is on a time limit, that gives them a finite number of rests they can take before. The other approach is wandering monsters: if the group tries to rest in a dangerous area, I make up an encounter (or I have an encounter prepared) and I use that.
In either case, I try to communicate the time limit or the environment danger clearly, so that characters don't overuse resources on early encounters.
To answer your question literally: you need to have a clear reason why the characters can't just long-rest whenever they want, and you need to communicate that in advance so that they know to conserve their daily powers. If they overuse their daily powers and then you decide their actions should have consequences because that wasn't what you wanted, they'll feel that you're being unfair.