The blood type diet recommends different dietary restrictions and ideal food groups for different blood types based on ethnic heritage. The basic premise is that the different blood types have evolved from different ethnic groups of people. If each blood type eats a diet closer to those ancient people then they will be healthier and experience less dysfunction.
I think the important thing with any diet or style of eating is that it works for you. Not all diets work for all people, but if the blood type diet works for you and you feel good eating those foods and avoiding others, that is great!