The person receiving the skin after the burn would be given these drugs most of the time because they dont want a ton of blood coming out of your body as your panicking or just sitting there feeling the pain which will make your heart beat faster in result of blood all over the place.
The person who has burn tends to receive the skin from donor. In this case the skin from another person needs to be adapted by the body of the recipient.
The skin from the outside of the body can be considered as antigen by the body and it can be rejected by the immune system of the recipient.
In this case, the recipients body is given drugs which suppresses the immune system so that the skin graft cannot be considered as antigen for the body and it starts making antibodies against it and ultimately the graft is rejected by the body.
