Winterizing: blow-out vs antifreeze for longer term storage?

I don't understand the logic of putting in the pink stuff only to blow it right back out. That does not make sense to me. I would do one or the other, but not both.

And if it were me, I would just blow out the lines (pushing a lot of air through), add pink stuff to the traps, and call it good.

I used to pump the pink stuff through, but went two winters (with temps well below 0 for a week at a time) with just blowing out and no issues.