With life support on, when you would normally die it will refill you to max health instead. This does come at a cost however.
For non-VIP players, the cost is 500 RP each time it revives you. For VIP players, the cost is 200 RP.
If you do not have enough points, even though Lifesupport is turned on, you will die, as you normally would.
This gives players a better chance to solo things like the Oil Rigs and the Cargo Ship.