If you set a high number of departures at a busy airport, they will all be injected at the same time, causing potentially 10+ minutes of constant uninterrupted chatter on the delivery and ground frequencies before you can possibly get a word in. It also causes unrealistic pileups on the taxiways. Having some reasonable delays between injections/clearances/pushbacks would clear this up and resolve to a more realistic traffic flow and less clutter on the frequencies.
This issue also affects arrival airports as the same thing happens when you get within injections range, and an unrealistic number of aircraft pile up on the taxiways simultaneously waiting for departures, making traffic flow at landing runways more cluttered than it should be.