One in 200 soldiers has the capability of fast healing themselves and others by touch.
The soldiers can regrow fully an amputated arm (theirs or others) in a matter of seconds but the process it's not passive. The healer needs to be concentrating on the process, granted it can keep doing other things (walking, talking, reading, etc) if practiced enough.
The amount of mass that can be produced by such healers, without rest is equivalent to three times their own body mass. The smaller is the wound the less mas is needed and the faster it will be healed.
1 - From a tactical point of view how would this special soldiers be used in a medieval setting? (would they be on a unit of their own?, would they be distributed amongst the other units?, would they be kept back or use in front?)
2 - How would the advancement of technology change their positioning? How would the positioning be different in an Victorian setting, what about a modern one?