The platforms are very narrow for the LIRR tracks, so holding 200% of a train (outbound and inbound) would be sheer pandemonium, and would practically guarantee someone falls off the platform. Even holding 100% of a train (just inbound, disembarking passengers) is already straining the platforms and methods of egress to their limits.

Holding even just 110-120% of a train load is very much a safety issue. I'm with the MTA on this one - the "mad dash" is horrifyingly inefficient, but is the safest course of action.

Of course, the correct fix to this is to fix the platforms such that passengers can wait at track-level without safety issue. But, of course, that's a multi-billion dollar problem nobody seems willing to touch.