As it shifts to the right, it means that haemoglobin has a lesser affinity for oxygen

The oxygen-haemoglobin dissociation curve, also spelled oxygen-hemoglobin dissociation curve, plots the proportion of hemoglobin in its saturated form on the vertical axis against the prevailing oxygen tension on the horizontal axis. The oxyhemoglobin dissociation curve is an important tool for understanding how our blood carries and releases oxygen. Specifically, the oxyhemoglobin dissociation curve relates oxygen saturation (SO2) and partial pressure of oxygen in the blood (PO2), and is determined by what is called "hemoglobin's affinity for oxygen"; that is, how readily hemoglobin acquires and releases oxygen molecules into the fluid that surrounds it. found on wikipedia

change in pH , temp. carbon dioxide 2,3 BPG shifts the curve

Leucocytes don't contain haemoglobin because function of haemoglobin is to transport Oxygen and WBCs don't have to transport Oxygen.

haemoglobin is important because it can carry oxygen.