The number of games I've won by going in 1v3 on an enemy team that overstayed to try to take an inhibitor turret after a won fight and died without killing any of them is literally in the dozens.
Why? Because I'm jarvan 4 and they have no escape from my ult. those 4 extra seconds i kept 3 members stranded in my base at low health as my 4 allies respawned to kill them, then proceed to 4v2 the enemy base or just take a free Baron - has definitely won me many games for a "suicide play".
It also doesnt only apply to this scenario - any time i can trap 2+ important targets that my team can get on before my ult expires is typically an advantage even if i have to die for it. Sure, ideally I'd survive but few allies can keep up with a tp + e-q-r j4 play to help me out.
Yes, dying isn't ideal. A good tank will start the fight and use everything then get out with 10% health. That can't always happen though - and if i can eat up 3+ ultimates while guaranteeing you're ability to reach the fight to clean up, my death was worthwhile.