too many red blood cells = polycythaemia / erythrocytosis.
as campbell said, reduced blood flow to the organs, increased risk of thrombosis, headaches, blurred vision etc.
too many white cells = Leukaemia.
All sorts of complications can arise from this, largely dependent upon what sort of leukaemia it is (acute or chronic), and which type of white cell has been effected.Complications can range from reduction in platelets and consequent bleeding/severe bruising episodes,, reduction of red cells, leading to anaemia and essentially O2 deficiency, problems with renal and other organs due to abnormally high quantities of white cell breakdown products.