Is it important before a blood transfusion to know blood types? Why? What are the benefits or consequences?

It is extremely important to know all types of blood because if you donate the wrong type of blood to another person, he/she will get sick.

Explanation:

Hemolytic transfusion reactions can cause the most serious problems, but these are rare. These reactions can occur when your ABO or Rh blood type and that of the transfused blood do not match. If this happens, your immune system attacks the transfused red blood cells. This can be extremely life-threatening.