The use of architraves for finishing around doors and windows is recommended for the following reasons:
Larger plasterboard sheets can be used, resulting in fewer joints.
Speedier installation of plasterboard.
Reduced chance of remedial work due to better placement of joints.
Architraves make best practice fixing of plasterboard much simpler. If the use of grooved jambs is unavoidable there are some golden rules to be followed.
The groove must be at least 1-2mm wider than the board that is being used. Trying to get a 10mm plasterboard into a 10mm groove will be difficult.
The back of the groove must line up with the face of the substrate.