By removing catchment areas for GPs, people can register for their preferred GP. This would mean that for those who would prefer a GP near work, then they wouldn't have to take half or a full day off work just to go to the doctor for a routine appt.
It would also allieviate the "postcode lottery". I recently moved from one part of Camden to another part of Camden. I was a 5 minute walk outside the cathment area for my old GP surgery. At my old surgery I had a good relationship with my GP, and could get an appt with my preferred GP in around a week.
At my new surgery I've yet to see a dr. It took 3 weeks to get my first appt, which was then cancelled due to Drs illness. My replacement appt is 4 weeks away!