I am wondering if it's entirely necessary to mortise a door and jamb for hinges and other miscellaneous door hardware. The only thing I can think of is that, in addition to being screwed in, the mortising increases integrity by locking the hinge in place provided that the fit is tight. Outside of that, it looks like it comes down to aesthetics and just looks nicer.
Well, let's take hinges for example. They typically have plates 3 or more millimeters thick and with two such plates it means you need a 6 millimeters gap between the door and the frame to accomodate the hinges. Do you really want a 6 millimeters gap? It will conduct noise, let unwanted cold/hot air through the door, it'll be very easy to put a crowbar and break the door open.
If you don't care of having a huge gap - no problem, you can install hinges without making mortises for them.
Most doors now are hollow core which takes away from the integrity of the door to recess the hinge. Even millimeters of wood make a difference over time, so I don’t recess and use a bigger screw. Recessing the hinges are for old school solid core doors for the purpose of barring the weight of the door. The door trim installed covers and gap and prevents weather from entering. If a thief wants in your house he’s getting in no matter the hinges. It also gives more room for the swelling and shrinking of the door because its wood and will do so. In my opinion it is completely unnecessary and weakens the design of the hollow core door. Now on solid core it’s absolutely necessary and needs to fit tightly to be beneficial.
If the hinges are not flush you will see light thtough the borders of the door. Ugly, unprofesional work. https://www.interiorsplace.com/why-do-door-hinges-have-to-be-recessed/