Those leftover box holes are annoying but easy to cover temporarily or even permanently if you don't plan to reuse the spot. I avoid messy mudding by using a flush-mount plastic cover with a clean edge—it sits almost flat and takes paint really well. The one I used last has a slight lip that grips the drywall edges so it doesn't fall out, and the door pops off if you ever need to reopen the space. After a coat of primer and wall paint it blends nicely without obvious seams. I recently grabbed a sturdy wall hole cover sized 8×10 and it covered my old outlet hole perfectly. Just trace the hole, cut if needed, and push it in—no screws required for basic installs.