> Nor is it customary to check for a "memory tight" condition and have programs restrain themselves, perhaps by starting fewer tasks in parallel, opening fewer connections, keeping fewer browser tabs in memory, or something similar.

These aren't mutually exclusive and are actually complementary with swap.

If you have more than enough memory then swap is unused and therefore harmless. The question is, what do you do when you run out? Making the system run slower is almost always better than killing processes at random.

And it gives processes more time to react to a low memory notification before low turns into none and the killing begins, because it's fine for "low memory" to mean low physical memory rather than low virtual memory.

It also does the same thing for the user. "Hmm, my system is running slow, maybe I should close some of these 917 browser tabs" is clearly better than having the OS kill the browser and then kill it again if you try to restore the previous session.