MCB are miniature circuit breakers that break/trip when excess current passes through the meter room to the MCB. Let’s say there’s some circuit problem like sort circuit, the current gets tripped in the MCB only without damaging the electric components in an apartment.
MCB is generally installed in the passage of every apartment. The connections/wiring done from this box to every room is also usually concealed in modern homes. But the main connections given to MCB board are kind a messy. There are few reasons for MCB being installed in passage area and not living room like-
The look of distribution box for electric line through that box is not good/messy.
The look and feel of the interior can be maintained in living room. I mean no home-owner would like to have a big box seen hanging in living room with so many switches.