After some thinking, I am wondering if having a 30% atmospheric oxygen concentration (or some other concentration) for a short time would increase the regeneration of energy in a body? It seems like it does have some mental effects, but I haven't found any other positive effects on the body.
Humans are pretty well suited to a 21% oxygen atmosphere (at STP). It's what our lungs are used to dealing with, and it's what brings the appropriate amount of oxygen to our brain (in particular, most organs are more forgiving, although not a lot more).
A lower concentration grows quickly and strictly deleterious, leading in short order to hypoxia, subsequently death. A higher concentration is also deleterious, leading initially to an oxygen high (as seen with Oxygen Bars), but also causing vision problems, seizures and death.
Oxygen is also highly reactive, and increased concentrations for even short bursts could, if frequent, lead to cancers, especially lung cancer. (The primary cause of lung cancer prior to asbestos and smoking? Breathing.).
There are cases in which increased oxygen concentration can be beneficial, but they are rare and specialised.