Answer
Active tissues will have a higher concentration of CO$_2$ and a lower pH. Hemoglobin releases oxygen more easily in areas with a higher concentration of CO$_2$ and a lower pH (for instance, active tissues).
Work Step by Step
The Bohr shift describes hemoglobin's oxygen affinity, which makes it more likely to bind with oxygen in higher pH areas and more likely to release it in areas with a lower pH. Since active tissues in need of oxygen will have a lower pH and higher CO$_2$ concentration due to their higher use of oxygen, this effect encourages hemoglobin to release oxygen in the areas where it is most needed and used.
