In a practical aspect of this, our 4th level party went through a bunch of combats without a chance for a short rest that brought everyone to single digits in HPs (most had fallen at some point) and two 1st level spells between the entire party. That was last session. Tonight we ended up having a battle with a cyclops justa few minutes later. At the end of that we were tapped out of everything. It was only about noon in-game but the DM was going to let us take a long rest.
We're on a somewhat time-sensitive mission, and I'm playing a rogue and suggested that I only short rest and blow HDs, and then can take watch for the rest of the time since we didn't need to actually sleep. Just to keep the time spent on the long rest to the minimum.
DM jumped to the end, and said that because I hadn't done anything too strenuous - basically stayed in the area and occasionally circled around keeping an eye out, I also got the benefit of the long rest.
Now, in this particular case it the DM was bending the "one long rest in 24 hours", and since the period was noon to the evening we didn't need to actually sleep, but that was an unprompted undeclared rest granted by the DM. Who definitely hasn't read this thread.