Advantages of a Factory Service Manual over an aftermarket Workshop Manual
Factory service manuals provide you with first-hand information as they are compiled and prepared by the manufacturer, meaning the people who built the car provide you with information about the car. Naturally, this means that you get exclusive information about your vehicle through a factory service manual that you would not otherwise get through a regular aftermarket workshop manual.

A manufacturer’s service manual will not have flaws or incomplete information. You will get precise information about your vehicle including the tools to use, the method to adopt, and the parts you will need to perform a repair job. Aftermarket workshop manuals are prepared by professionals but they are created through trial and error, meaning there can be some methods in there that are useful but some tips or tricks might damage your car rather than repair it.
Moreover, factory service manuals are extremely detailed and compiled professionally. You get in-depth knowledge about any and every problem that could arise in your car. These manuals even go as far as suggesting the right tool to perform a certain function. What's more, you get recommendations as well as a suggestion about when and how to maintain your car.
Some manufacturers might even provide you with the service manual for free depending on the vehicle you buy. If you get a manual for free that is a bonus since you won't have to pay anything extra. There are also websites that offer outdated factory issued workshop manuals for free download. Otherwise, you would have to pay money and either buy a factory service manual or an aftermarket manual.
A factory service manual will come with detailed diagrams and explanatory paragraphs defining the process of repairing. Aftermarket service manuals lack such information, and they are often oversimplified. If you are just starting as a DIY-er then a factory service manual is the only thing that will do you good. Otherwise, you will be stuck in the middle of a repair, possibly doing more harm than good to your vehicle.
Factory service manuals are vehicle specific, so whatever information you get in the manual will be related to a particular car. You can find workshop manuals that are vehicle-specific, but they are not available for every vehicle. If you have a brand-new car or a very rare vehicle, you might have problems finding an aftermarket manual. Therefore, you have to depend on the manufacturer to provide you with the service manual.
Yes, factory service manuals are slightly more expensive than aftermarket workshop manuals, but they are worth every penny. With the detailed information they provide, you will save more money in the long-run.
Conclusion
Factory service manuals provide great relief if you are an upcoming DIY enthusiast that is looking to make their car repairs. Yes, you will have to spend money, but if you come to think of it, a service manual will save you more money than they cost.