What kinds of repair needs do you usually run into that require vendor's technicians? Is it e.g. electrical, or are they the stereotypical "everything is a comp

What kinds of repair needs do you usually run into that require vendor's technicians? Is it e.g. electrical, or are they the stereotypical "everything is a computer" type of problems that everybody complains about in cars? Can you try to fix even mechanical problems yourself, or are those typically not the issue? Asking out of plain curiosity.