Varnishing in steps?

Q: My husband and I are having a debate as to whether or not we can varnish our oak hardwood floor one room at a time.

I think it would be OK to do this, since each piece of wood would take the varnish differently. He says, that we have to do the whole place at once, so we are not left with lines where we stop and finish.

A: It can be done if you stop along the edge of the board. However, if you are applying across the grain, you will have a line.