Bascially if GE2019 had been fought on these boundaries then BoJo’s majority would have been between 10 and 20 seats larger. This is because, of course, the opposition parties would see a decline at the same level thus increasing the gap by double the Tory seat gain,
These probably won’t come into effect until Q3 2023 thus increasing the speculation that there could be an autumn general election in that year. Also the fact that the Tories have this bonus “in the pipeline” makes it less likely that there would be an election on the existing boundaries.
Of course much can happen in the meantime.