It can mean a lot.
This is an important factor to match up for a transfusion itself so there is no antibody
reaction from the recipient if they are rh neg.
And donor is rh pos.. It is extermely important in women of childbearing age who are rh neg. To be sure they get no rh pos. Blood so there is no chance that they develop antibodies in case they have an rh pos. Child and so have hemolytic disease of the newborn.