The body does not store oxygen. Athletes who inhale a few minutes of oxygen, and then return to the playing field, are not benefitted in any physiologic way. To give more oxygen requires a hyperbaric chamber, an expensive piece of equipment found in relatively few hospitals. Supplemental oxygen is a drug. Like any other drug, it has indications, contra-indications, and side effects.
Supplemental oxygen is the most commonly prescribed drug in hospitals.
A reduced PaO 2 is a non-specific finding. A low PaO 2 should not be used to make any particular diagnosis, including pulmonary embolism. High FIO 2 doesn't affect COPD hypoxic drive. The reason a high FIO 2 may raise PaCO 2 in a patient with COPD is not because the extra oxygen cuts off the hypoxic drive. The actual FIO 2 with nasal oxygen depends on the patient's breathing rate and tidal volume, i.e., the amount of room air inhaled through the mouth and nose that mixes with the supplemental oxygen.