No need for so many words. It's alt-fire can heal your vehicles and team mates. first fire is a normal weapon but no one likes first fire. Its alt fire can grill your enemy too
shutdown_
Actually, the alt fire does not heal your teammates, but rather it causes their own link gun to become more powerful. If someone you are linked with is using alt fire, then it can heal vehicles or build Onslaught nodes faster. If they are using the primary fire, then the plamsa projectiles become much more powerful (and turn yellow rather than green). When linked, the primary fire becomes an awesome defensive weapon. You can link several people together a well, to increase the power of the link gun, but I don't know if more that 3 people links does much good.