I will admit that pne of the goid thing abput forums is experiencing different paradigms.
I dont think i can recall any time where players in games i GM or played in where an 8 hour rest in "a dungeon" (or analog to any uncontrolled hostile situation) would be attempted.
Even if they/we had some form of cover like spells for huts or whatever, it would have been rare that we wpuld think in an already active situation we would have the time and the enemy so few options that we would see it as a successful path.
One of our tangential groups was very much into the 5 Minute Workday back in the 3e era. They would constantly rest, either by fortifying their positions with spells or by retreating, resting and returning. It was way overkill for most of the challenges, which the DM ended up making tougher as the campaign went on. It was a pointless arms race. I only occasionally played in that game and didn't much care for it.
In our current groups, three campaigns with three DMs, we all favor extremely large 'realistic' dungeon complexes that are sparsely populated. Monsters and encounters can be hundreds or thousands of feet away from each other rather than right next door. Wandering monsters, exist, but there is a lot of potential room to set up an ad hoc camp to believably grab a rest. Spells, such as Leomund's Tiny Hut, can also make this pretty easy.
One DM tends to mitigate this urge with adventure-specific time factors (the curse in the castle is getting worse, the volcano is getting ready to explode, the demon lord is doing nefarious things). This works occasionally, but there's often an odd tension. He creates a large meticulous dungeon for us to explore, but then pushes us to not explore by emphasizing the time limit ("Do we have time to investigate this room?" "Sure, the demon lord won't complete the ritual for 40 minutes, we've got plenty of time to save the town").
I tend to favor dynamic situations with a rival or enemy force in the same area at cross-purposes with the party. That usually keeps things moving. I rarely use dungeon exploration as an activity in my games, barring as a location for a quest MacGuffin that must be found or as an attrition gauntlet that must be passed through (like the Mines of Moria).
Back on the subject of Slow Natural Healing, and player psychology, I do think the lack of comprehensive retreat rules in D&D play a part in players wanting to be at full hp at the start of every engagement and doing whatever it takes to achieve that. Once a combat has started it's almost impossible to get away from it without being severely punished. Starting at, say, half hp already strips away a 1-2 round buffer to get things done. At half hp and a couple of bad rolls you're looking at PCs on the ground. Once that happens, the chances of a TPK increase significantly. Combat is usually an all-or-nothing affair and once the PCs are 'pot-committed' by losing a ton of hp, using a bunch of spells or having downed PCs in irretrievable positions, it's often hard for them to choose to take the punishment of retreat round OAs (and possible chase) just to forfeit all that for no gain. A lot of players will just roll the dice, hope for a hot streak, and fight on to a TPK.
A lot of the above is predicated on the DM's style. The DM decides the ease of which combat can be avoiding in the first place and the ease at which it can be retreated from. If the DM gives players options and opportunities in both these areas, adventuring at less than full resources becomes more enjoyable and less of a unfair death crawl. Riskier, certainly, but doable for the clever and the bold.
