In order to remove all fuel, lines must be blown out, or enough fuel will remain to cause problems. Second, draining exposes the bare metal in the tank and fuel system to air and moisture which causes rust and corrosion. Third, gaskets and seals may dry out or crack, leading to leaks when the system is refilled. Lastly, drained fuel is a fire and safety hazard and proper disposal is difficult. For these reasons, draining is not the solution.
Fuel stored in gas cans or tanks also gets old, oxidizes and breaks down.
You might be left with bad gas. Using the same fuel next season greatly increases the likelihood that deposits will form in your equipment's fuel system. Prevent this problem - stored fuel should be stabilized too. STA-BIL keeps gas fresh for quick starts. It's a blend of scientific additives which prevents fuel from undergoing degradation and oxidation during prolonged storage.