I have seen seats reserved between Manchester Oxford Road and Manchester Piccadilly now THAT is silly
It is silly, but when you want a ticket from Oxford Road to (say) Birmingham New Street and get a seat reservation for the XC leg, the online booking system will generate a seat reservation for the connecting leg from Oxford Road to Piccadilly assuming the connecting train is a TPE/EMT.
Similar in a way in Scotland where you could book a ticket from Haymarket to Newcastle, changing trains at Waverley to a VTEC/XC starter, if the connecting train has seat reservations available [for example a long distance Aberdeen/Inverness - Edinburgh service] you could end up with a "Haymarket - Edinburgh" reservation which 99% of the time won't get used due to the frequent nature of services between those two stations.