One of the things I notice: Most measures against 15 minute adventuring days or 5 minute nova loops also affect more "reasonable" play. What do you know if the party really exhausted some resources and don't think they can risk more fights?
Who gives the players a guarantee that the GM has designed a dungeon or scenario that it has exactly the x encounters that the players can handle, and not spend one more? Maybe they had encounters the GM hasn't originally planned (with all those random wandering monsters, or because the players wanted to try something), or the GM has miscalculated, or the GM actually intended for them to be able to rest without risking failure.
But how would the players, or the characters now? After they lobbed their last fireball against the Hobgoblin unit defending the courtyard, they definitely know they are out of fireballs, don't they? But do they know there are only two more encounters that can be done without another fireball? If they don't, wouldn't they have to consider the risks of the enemy shoring up defenses or rallying support against them vs. rushing in exhausted and weakened by the previous fights? Maybe the necromancer gets his evil sacrifice done and summons a bunch of extra undead. But the party being dead won't stop him, either.
The Goblins bribing some Ogres to aid them might be a nasty surprise - but with two fireballs and full hit points, maybe that's actually less of a risk than fighting a bunch of Goblins without them? This becomes more pronounced as you grow in levels, even, because the difference between "spent" and "Not spent" increases considerably.
Attrition also works both ways - the enemy troops have been thinned out, too. Maybe they can get more troops, but maybe they can't, while you did in fact gain resources by resting. Comparing perhaps to going back to town to acquire some hirelings or ask the local militia for help for a Raid against the Goblins terrorizing the town.
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Basically, balancing the game for "adventuring day" puts also a lot of onus on the GM to adhere to it, reducing their freedom in how to build his adventures or campaign, or accept that the game will be imbalanced for certain classes.