BA still do it on most flights, those short haul flights with only 1 rotation per day they don't but they do on all long haul flights, especially to america where people can be re-routed through say JFK then connection with AA. I know this for a fact as teh last flight i was on to BWI was overbooked by 16 passengers going out and 25 coming home. People were upgraded to Club World and Premium Economy then the rest were re-routed or placed on the following days flight which then made that flight overbooked. Works for them most of the time as people either don't show or change their flight plans last minute or their incoming connection is delayed.