You will always have a job, since people will always need cars. Even when we move to self-driving cars, there will still need to be people that can fix them. This translates to job security, which is the largest benefit of being a mechanic in my personal opinion. You also learn to build a solid work ethic, and understand how to think through things critically while under pressure. You learn logic, and how to work with others. You also gain the ability to be technically and mechanically inclined, which helps translate to other fields and things that are similar to a mechanics line of work.