There are three ways to do winterizing.
1. just blow out the lines.
2. just put antifreeze in the lines.
3. blow out the lines and then put antifreeze in.
I do the 3rd because I do not want to have to fix a leak somewhere in the wall of the RV.
Blowing out the lines gets rid of most of any water. The problem with just doing that, leaves some water in the lines especially if you have a low spot. Just doing antifreeze, it will mix with the water in the line and possible give you a weaker mixture. I say possibly.
Suit yourself, all three work and at most about 1 hour of work and maybe 3 gallons of antifreeze.