The main benefit the Garmin offers is recording your track so you can upload it to your computer or a website and see where you've been, your speeds, cadence and HR at various points along the ride, as well as the elevation profile along your ride. Non-GPS computers can't record your track, but some do record your speed, cadence and HR as function of distance or time. Most only tell you your current parameters and the average for the past ride.
Another feature of the Garmin 500 is you can download a route to it which can be depicted on the screen as a breadcrumb track that you can follow, though it won't show any roads. You can also set up a virtual training partner which you race against, training workouts, etc.
Most if not all this functionality is available on smartphones with appropriate apps and accessories. Smartphones also will have maps, where the 500 will not. You will need to go to a 705, 800, or 810 to get maps on a Garmin Edge.