Will you still be seated after the show starts?

If it's a Broadway show, the tour may require the usher staff to keep you outside the auditorium during certain songs/scenes before you can be seated. This is to ensure that quiet moments are not disrupted and light from the doors doesn't ruin any special effects. Generally after the first few songs of the act, you can go in and out freely.

You can be seated at any time, and there are many employees to help find your seat

Folks were in and out almost constantly in the cheap seats for Wicked.

Depends on what show you see and your personal preference, but the seats are super comfortable and the show I saw was fantastic.

I believe it depends on the performance