The oral inflator provides the diver with the following options:
1. In conjunction with the auto-inflator it can become a third regulator.
In a worst case scenario of rescuing two out of gas buddies, a skilled diver can depress the auto-inflator button while holding the oral inflation button in the open position and breathe quite well. Also, if a diver had two second stage failures such as a torn diaphragm along with a clogged second stage, a diver could use this method to breathe. More commonly, if a diver had a primary regulator torn from his or her mouth by an out of gas diver and could not find a back-up or octopus quickly enough, the diver could revert to breathing from the BCD.
2. BCD inflation without the need for air/gas in a scuba tank.
Following an emergency ascent or an air-sharing ascent, a diver may need surface floatation. Without an oral inflator, it might be impossible to get air/gas from the cylinder to provide enough lift or do so in an expeditious manner. By taking away the oral inflator, a secondary method of inflation such as a CO2 cartridge would be necessary in that event. By removing the oral inflator and adding a CO2 cartridge, you increase the potential for serious injury and death.
During an out of gas ascent, a diver may be controlling buoyancy to stay with the donor and accidentally vent too much. The oral inflator will allow the diver to add air to the wing or BCD to correct for this loss.
During a deep emergency ascent or a situation in which an out of gas diver cannot kick such as if suffering from DCS, a diver may wish to orally inflate underwater and use the wing or BCD for ascent.
3. BCD inflation in the event of a low pressure hose malfunction.
Should a diver experience an auto-inflator malfunction requiring the diver to disconnect the auto-inflator, the oral inflator will allow the diver to achieve neutral or positive buoyancy easily.
4. The oral inflator is a secondary dump valve.
While most well-trained technical and cave divers use the OPV/rear dump to vent gas from their wings or BCD's, the oral inflator is a secondary dump in the event of a problem locating the pull cord or a malfunction of the OPV/rear dump. It is also a preferred dump valve when ascending in a verticle position such as in a cave chimey that would not allow a horizontal body position during ascent.
5. Educational tool.
Unless the majority of wings and BCD's in the industry removed the oral inflators (which would be farm animal stupid), instructors and students would need to be equipped with a BCD or wing that allowed them to demonstrate and practice the skills that incorporated the use of an oral inflator. A BCD without an oral inflator would find an extremely limited market to begin with and to remove its use by instructors and students would further hamper its marketability.
6. Alternate inflation source when everything is working normally.
Sometimes a diver finds a reason to inflate orally when all is working normally or just wants to play or practice the skill of oral inflation.
7. Inflation when auto-inflator is operable, but disconnected.
Divers using closed circuit lift bags and DSMB's may wish to inflate these markers via the Schrader valve in warm water when not diving with drysuit or additional low pressure hoses. The auto-inflator hose may be disconnected for that purpose when the diver will need to add gas or air to the wing or BCD. Without an oral inflator this would not be possible.
To solve any need for a secondary method of delivering gas into a BCD or wing, a second auto-inflator would need to be part of a BCD system. Two auto-inflators would add needless complexity to a BCD or wing system. A diver facing a stuck auto-inflator problem would waste time determining which hose was the culprit and possibly face a runaway ascent if unable to resolve the issue quickly.
