Constant lifetime is nice.
But:
1. Particles can go offscreen -> useless to update them
2. Particles can have alpha <= 0 -> useless to update them
so in both cases they better get killed early unless you want to ensure that low end system (casual systems) don't play your game.
But:
1. Particles can go offscreen -> useless to update them
2. Particles can have alpha <= 0 -> useless to update them
so in both cases they better get killed early unless you want to ensure that low end system (casual systems) don't play your game.