What can i gain from alternative nostril breathing?

If ur normal, nothin: Breathing into one nostril while holding closed the other nostril will gain you nothing if the anatomy of your nose is normal theoretically if you have a deviated septum or a "hole" in your septum (say from use of cocaine) holding one nostril closed while inhaling air could give you better oxygenation, though i doubt you would want to walk around holding a nostril all day. Have a dr, examine you!