Funny story...

When I was a new hire, I was sloted as the Lead FA. We got a ~3 hour delay notification from the app whilst still at the hotel, due to a delayed inbound at an outstation. My (senior to me) coworkers convinced me it meant we could go back upstairs and take a nap. So that's what we did. Until the scheduled time that we were meant to be boarding, when I get a call from crew scheduling wondering where the heck we were as we were meant to be on the plane at that moment. I muttered something about being in a bathroom and ran downstairs, called my coworkers from the front desk, we piled into a taxi and made it to the gate ~30 minutes later. Turns out the crew scheduler called the wrong flight's Lead FA after she juxtaposed an employee number. Same airport, very similar departure times and flight numbers.

Got called into my supervisor's office anyways as I was still on initial hire probation, and was given a stern warning to never do it again without being in contact with scheduling. "The operation changes by the minute, and delays can sometimes turn into on time arrivals, but only if the crew is there on time and ready."

Plane swaps, ATC clearance changes, crews waiving duty limits... the list goes on and on. It's your choice whether or not to be there, but certainly don't be upset if you were left behind after something comes up and pushes the departure time back closer to normal.