Modern digital cameras produce very good jpg files, however they often can be improved, particularly in shadow detail, color balance, sharpness, and a few other areas. If you try to make these improvements to a jpg image, you are already starting where the camera software quit. Since the camera software already "threw out" much of the data from the sensor when it produced the jpg image, adjustments may be difficult or impossible.
If your camera can produce a RAW file, you are starting from scratch with the data from the camera sensor. You have complete control over white balance, shadow & highlights, and many other editable characteristics of the image. Depending on your editing skill, you may not be able to improve on the camera's jpg producing software, but with practice, it doesn't take long to be able to produce better results than the camera software, particularly under difficult lighting conditions.
In the past, most of the editing & manipulation decisions were made during the printing process, either by machine, or, if you were willing to pay for it, a skilled enlarger operator. Since digital removes the "manipulation during printing" that was done during the film days, if you want or need it done with a digital file, it is going to be up to you (unless you send the file out to be custom printed).
While many individuals have no need or desire to go any further than the image the camera produces as a jpg, I consider photography a hobby. Like other hobbies, how deep you want to get into it varies with the individual. There does seem to be a significant number of camera users that are interested in editing their images - the Photoshop Elements classes I teach rarely have an empty seat.