Originally Posted by
agehall
Don't use the term "link" - it makes people think you can do things you cannot. TCP (or To Complete Party) is a way to allocate seating for another PNR that is traveling along with the GCH but not on the same PNR as the GCH.
As far as I know, it offers no other benefits than this.
This is not correct. TCP is an Amadeus command to link bookings, effectively putting a reference from one to the other. Anyone can have this done, it is not limited to GCH's (for BA), but as you say does not provide any benefits.
GCH seating requests for separate bookings will have a TCP done and then sent to the back office to have seats changed on the other booking(s), but this is not part of the TCP process.