How long do you set the time on the clothes washing machine?

I used to set the time on the medium amount, which always appears to be the recommended setting on machines. However, for some reason, when I moved into my present rental house with its own old washer, I’ve always set it on the maximum amount of time so that the clothes will agitate as long as possible. I have no explanation for this behavior.

My clothes get clean, but am I wasting energy? Would they get clean on less time?

I don’t have horribly dirty clothes. I would call it normal wear and tear. I do wash clothes for my teenage daughters, and theirs tend to have more odor.