They have an obvious advantage and so will earn more in the long run, that's pretty clear! Also playing together and playing both separately would lead to the same amount money, so they are not risking more money just together (same argument for the profits.)
Now I don't really know to much about collusion and specifically what edge it can give you but I suppose situations such as this would be pretty profitable.
Assuming they share all the money at the end lets and imagine (for simplicity) we have only 3 players.
Colluding Player A (A) 500
Colluding Player B (B) 500
Smuck (S) 500
The hands are:
Colluding Player A (A) AA
Colluding Player B (B) --
Smuck (S) KJ
S- raises 150
A- Comes over the top all in.
Now lets pause and look at the two different situations. I player B was not colluding then he would fold and player S would have the following situation:
Pot odds: (700/350)=2:1 so they need a hand with 1/3=33.33% against player A to call. Now that means that they have to put player A on pockets 10 or worse or QJ or worse. This is a pretty easy fold and Player A does not get paid.
Now lets suppose that player B is colluding and now also moves all in. Now player S has this situation:
Pot odds= 3.3:1 so they need to have a hand that wins 23% of the times to make this call.
Player S is much more likely to make this call (based on pot odds) as long as they are not both holding QQ+ or AK, AJ the odds are pretty decent.
Now the colluding players should take the money and both make 250 as opposed to not colluding where player A only takes 200 a profit for both players!!
So a bit more accurately assuming a fold in the first case A make +200
In the second A make (500*0.85)/2=212.5 and so does player B (just accounting for when S wins the hand)
This is just a toy example of when it can be useful!
Thats just one example of how