You get different sex scenes when you revert to earlier ATs because, to an extent, they go back to their earlier schedules and events but with increased permissions. Like when Gina wouldn't allow penetration during the massage thing she's fine with it or sex at the bar at the end of the night.
In theory it would also allow for more lateral movement along alternate AT paths but those haven't really come up in ages and with the slow pace of SP2 and Loser due to split attention it'll probably be quite some time before we get anything along those lines.
