Each Seat is for one individual user who uses their Adobe ID to activate the software. That Seat allows the individual to activate the software on up to two computers, but not running at the same time. This is the same license for activation that comes with an individual purchasing a perpetual license (serial number).
So it is not the installation that is limited but the number of activations. If the individual activates on a third computer they will be asked to deactivate on the others, and and then reactivate the second computer when using it again.