I think we need to stress that it is a very weak link between bookings, more of assistance for an agent peering into a booking to resolve something. Agents don't normally have the time to do this, only by exception, basically. So TCP won't on its own make a big difference to upgrades / downgrades, often they are looking for single passengers for upgrades to increase seating flexibility in the lower cabin, so TCP could increase the chance of an upgrade in the first instance. Where it makes a difference is that if it happens, and you go to the desk to complain about it, the agent can see the TCP and will then be able to resolve the case, even if it means someone else gets the upgrade. If they were bumping someone off the aircraft altogether - a rare event these days except on a few routes to Africa - then TCP would more or less ensure that the entire party stays together, whether on or off the aircraft.