Simple Senerio.
Soldier on your team is injured so you send him to the medic on your team to be healed. While he is being healed he is shot and killed but Medic will not stop trying to heal him. You can order the medic to move but he won't, he just tries to ressurect the dead body. You can tell him to reload, go get ammo, etc. and he will but then goes right back to healing the dead body. While he's obessed with the dead body he will not heal anyone else.
Doesn't happen that often, but I was shot in the leg and couldn't stand, and my medic was busy with the stiff so I had to crawl for 1500 meters to the extraction. Not fun.