a)-Theoretically yes, practically not necessary, it all depends on how good you are in electronic repair knowledge. For a beginner it is a 'must' for you to understand about schematic diagram, as you gradually gained more knowledge you will automatically depends less on schematic diagram. You will definitely need a schematic diagram when you come across a new designed or technology. For example, when comes to crt monitor repair i seldom see schematic because i already understood most of circuitry and section in a crt monitor. The new technology such as lcd or tft monitor makes me have to temporarily relies on schematic diagram. As my knowledge of lcd monitor repair grows, i will gradually depends less on schematics. May be my situation is different from yours because i'm concentrating only on one type of equipment. I've seen quite a lot of repairers in my country that repair many types of equipment such as tv, video, vcd, dvd, amplifier, hi-fi, fax, laser printer, microwave and so forth. Most probably they need schematic diagram to keep them up to date on each of equipment technology.