allow vs allow for

In that sentence, "for" is not necessary.

To allow for means to take into account when planning something. If you are planning to drive from the East Coast to the West Coast, your schedule must allow for time you spend sleeping instead of driving.

Not necessary but certainly possible.

Which sounds better?

I'd say both, depending on nuance. Off the top of my head, with not too much thought, "allowed for" sounds like a special provision has been made for something.

I could be mistaken.

Good'n, Cam