Why Blood group antibodies not importance during transfusion

 It is because transfusion is done where whole blood is not transfused, just the individual components such as red blood cells, plasma, or platelets. If whole blood is collected, it is then centrifuged to separate the components, and stored that way.

The antibodies are found in the plasma portion of blood, so when type A red cells are transfused, there is hardly any plasma present because it has been removed, so there is not a reaction. If you were to transfuse type A plasma to an AB individual, it would cause a reaction, because the anti-B would attach to the red cells and lyse them (break them apart).