If you usually keep your squad’s stamina high and avoid aggressive opponents, then injuries are sporadic. Even if it happens, the downtime will be only one or two matches. That’s why there is no reason to buy rare healing items which reduce the downtime in five matches.
The common healing item should only be used if you need a player, in particular, that’s got an injury. Most of the time, you can avoid using healing items if you own quality backup players. You can put the injured player in the reserves and replace him with another.