This has been discussed in years' past. I remember the following notable comments and observations from people:
- For reference, Volkswagen specifies that oil drains can be prolonged until it slows down to one drop every 20 seconds.
- For some engines prolonged drains can drain the oil pump to where it loses its prime. The engine will not develop oil pressure for quite a while on the first startup. This is likely only a rare occurance.
- There is still a good amount of dirty oil that will never drain from the lifters, oil galleys, and other dead spots, so getting the last few drops out of the pan can be rather moot in the grand scheme of things.