Don't use you're lifeline ult when you're the last 3 squads left. It basically paints a bullseye on your head, and tells everyone to come kill you. If you do want to use it at that point, don't use i...
I could see it also being used in the middle of the fight, I mean when it comes down, it makes a pretty big smoke plume, and if someone is actually gonna try and go for it in the middle of the fight, they could be putting themselves at a massive disadvantage, plus it could block off a way for the enemies to come.