The Rebels only want 4 teams as well, I assure you. Just as long as they are one of them.
 
If another team folds, for the sake of the argument let's say the Waratah's 

 , it means that a team full of solid Super Rugby and Wallaby players suddenly come onto the market for the other 4 teams to divide up and bolster their respective teams.
 
That means we have 4 Oz teams that have a lot more depth. That doesn't equate to competitiveness though; coaching capability is another question for another time.
 
It also means we can skim the best of the ARC/SS/etc, rather than pluck out players that just aren't ready (or capable) of Super Rugby, just because we need to fill our team roster/injury cover.
 
I'm sure there are other minor details around money/tv/central control/whatever, but I could give two fucks about that.
 
The player reallocation bit makes sense. Sadly, one province is going to be sacrificed to make this happen.