Herod
The rule in the UK now is that, with the new locked door policy, if you leave the flight deck, one of the cabin crew has to "baby-sit" the remaining pilot.
Maybe with your outfit, not at Big Airways, and the basic reason was that you had to get out of your seat to let the person back in. Our arrangement was that at the start, but we now have CCTV outside the flight deck, so that the other pilot can see the galley area and the person requesting access from their seat. Now we are free to come and go thanks to the camera - a much better situation all round, but still not as good as the old days.