Hi C_Star,
How about balaning fuel in case of engine failure? In my outfit we are taught to switch the x-feed on and keep all 4 pumps in to draw fuel from both tanks to the live engine. In the sim it works like a charm.
If you have an engine failure, and keep the fuel X feed closed, the fuel imbalance will still grow at the rate you are consuming fuel by your running engine.
If you open the fuel X feed (with no fuel leak), then the imbalance rate cannot be any worse (it may even be less if you have a stronger pump on the dead engine side). The benefit is all the fuel is now available to your only running engine. You won't starve the engine until all the fuel is exhausted.