Do I have to sand my hardwood floor in order to refinish?

We found that we have hardwood floor under our carpet. We prepped the floor by taking out the floor tacks and staples. We went to rent the floor sander and the guy at the store said that it would save us money on sand paper to strip the varnish first and then sand the floor. So, we now have the floor stripped of varnish and we plan on staining our floor a dark dark brown. Do we still need to sand the floor since we stripped the varnish, or can we just wipe it down and start staining?