Watch this video up to minute 3:00 for an introduction on why resumes are useful.
Resumes are a great way to keep track of all the important details regarding your work experience, such as specific duties or dates so you can easily refer to that information when needed.
It's useful to create two versions of your resume. The first is a master resume which includes all of the jobs you've ever had, along will all skills and other experience. The second is a one-page resume specific to the jobs you're applying for, which only lists the most valuable experience you have.