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Quoted from Linus

[…]

well yes, but doesnt it just recharge the sandvich “ammo”?

Indeed.

Players can use the alternate fire key to drop the Sandvich onto the floor. A dropped Sandvich appears on a rotating plate and acts as a medium-sized Medkit that can be picked up by both allies and enemies. The Heavy cannot use a dropped Sandvich to heal himself; picking up a dropped Sandvich will simply reset the cooldown timer.

http://wiki.teamfortress.com/wiki/Sandvich