I do so, somewhat, in hammocks as it keeps me from sliding footward during the night and smashing up against the hammock end, necessitating a struggle to wriggle upward and get stretched out again. Tying the foot end a little higher takes care of this and means a much more comfortable night.
On the ground, when the site is sloped I prefer to have my head uphill, period.
Backpackers can borrow a self-massage technique from long-distance cyclists that I’ve found hugely helpful in bringing tired, swollen legs back to life. Lie down, face up, with your legs elevated against a tree or some other support. Beginning at the ankles, massage each leg, working towards the knees. This helps force accumulated fluid out, presumably including lactic acid.
I don’t know how much science there is behind the technique, but I can testify it’s helped me stop cramping and seems to lessen pain and stiffness the next morning. I’ll sometimes use it on rest stops during the day.