Most of the services (FlightAware, Flight Radar 24, ADSB Exchange) get much of their data from volunteer-operated receivers. If you feed your own data to these networks, you get several benefits including multilateration capability (computed location for planes that don't send their own GPS location data) and free business accounts on FlightAware and Flight Radar 24.
FlightAware in particular gives you access to a greater level of data and services on their site if you're an active contributor via a PiAware.
Also, honestly, it's just fun fooling around with the antenna and software setup to maximize the number of flights I can see :)
