If I get above 8500 feet, after about a half an hour (varies), I start feeling uncomfortable. I'm lean, reasonably healthy, but older. I did a west coast to east coast trip 2 years ago and was occasionally forced up above this altitude for short periods of time. When this would occur taking frequent hits on the canned oxygen (Boost) really helped me feel better.
Also, even on long trips at lower altitudes I will take a few hits off it and I feel a little "clearer". This is the first time I ever heard anyone say this can be beneficial at low altitudes. It was just something that seemed to help me.
I always keep a larger can (bottle?) of Boost in the plane and use it regularly.
You certainly can't go up to higher altitudes and think it's going to help you there for any extended time. The can doesn't hold that much. But two or three hits certainly helps me in the scenarios I described.