Clearing a container is usually a much simpler and faster operation than looping through all and removing them individually. That's not a question of tidying something up.

There were compiler optimizations for clearing by iterating. I haven’t looked at the code, but I suspect this won’t be much more efficient than iterating was with the optimizations.

I expect both will result in the same code; the only difference is that the clear built-in can handle maps with NaN keys.