What do these changes mean and what is an impacted line? The clue is in the checker text which refers to a bridge tap and wiring issues. In laymans terms an impacted line is one where the VDSL2 service is running slower due to the presence of telephone extension wiring, or other things like non-twisted pair wiring in a home, or bad practice wiring (e.g. not using a coloured pair, but a wire from two different pairs). For the first four years of the FTTC roll-out these issues have largely been avoided, since the engineers arrive and install a filter faceplate and install a dedicated data extension if it was ordered. Once self-install becomes common we expect to see the same wiring issues cropping up that have regularly seen people with ADSL and ADSL2+ getting lower speeds than they should.
So what is to be gained by having a self install? You might save a few bob but forever have a lousy speed. Of course it might not be all coming up roses if a contractor does your installation.