Every automobile manufacturer has their own way of identifying each and every wire, connector, splice, ground, component, etc. Becoming familiar with how to identify each circuit component will help you to become better at reading diagnostic instructions and following the schematic too. Becoming familiar with how to identify each circuit component will also help you document your work. Writing "locate and repair short in horn circuit" on a repair order might sound all right to you, but what if you could write "locate and repair short to ground in horn circuit 784 between connector C101 and C124". The later description sounds more professional and in the future it may allow someone else to identify the area you have worked on should trouble arise. On the other hand it could prevent you from having to work for free on a "come back". If the horn acts up again and you find a different problem, your previous documentation will help clear you of any misdiagnosis accusations.