than a medic who has to wait until everyone's dead to be useful.
First of all, i don't know why everyone seems to think that medics are only useful for revives, when they can give you three different buffs, transfer supplies to you, and oh I don't know, HEAL YOU. Not all medics wait until your dead to help you, I for one like keeping you alive more than reviving you when your down, It just feels like I am doing my job. Sorry, I just had to get that out.
Now, for the OP's question. I use Transfer Supplies as one of my three abilities, and I think it's a pretty good ability. I use it when I have a good amount of pips and no one needs immediate medical attention at the moment. And I give it to either a soldier or engineer. (because I know that operatives don't really need it). Or I'll give it to someone in return for a weapon buff or ammo. Also, I will give it to another medic who is low on supplies when I have a good amount. It gives you a nice chunk of XP, and helps others out. It just takes getting used to use it routinely, like other buffs and abilities. And to answer your other question, you can't tell when they have exactly zero pips, but it won't let you give it to anyone who is not low on pips, so anyone you ARE able to give it to, could use it.