Synthesize the concept of the threshold effect in hemoglobin and its significance in oxygen release to tissues.

The threshold effect has no impact on hemoglobin's oxygen release to tissues.

The threshold effect prevents hemoglobin from releasing oxygen to tissues, reducing oxygen delivery.

The threshold effect allows hemoglobin to release more oxygen to tissues with lower oxygen levels, optimizing oxygen delivery.

The threshold effect causes hemoglobin to release oxygen only at high oxygen levels, limiting oxygen delivery.