In the US there are staff in the aisles of each section. Some venues are more strict than others about being in the aisles, some will let you move up in the aisleway to take a few pics and then go back to your seat and others won't let you into the aisles at all unless you are leaving the arena floor.
As for the chairs most people leave them with the seat pushed up so there is a bit of space to dance a bit in depending on the people around you.