As the name suggests, workshops can repair, clean and change your vehicle's color type. This will come very handy in case you are being chased by other players and your vehicle is about to break down.
You can purchase vehicle boosts (NOS) to increase your acceleration for a brief moment. Vehicle kits are available to buy too, these can be used to repair your vehicle anywhere on the road. Another item you can purchase is Armored tires, which will make your tires bulletproof (just remember, they are still vulnerable to spike strips). Alternatively, you can purchase a truck and truck trailers to help yourself begin with truck deliveries. Specific workshops (located at Sandy Shores, Los Santos International Airport and Fort Zancudo) will also allow you to purchase Aircrafts.
You will find these workshops around the map with the icon: 
