Unsure what you really want to know.... seems like a pretty general question.
If you are in a completely immersive environment (i.e. can't see "reality"), you may hit "real" objects since you can't see them. and be somewhat surprising when it happens. However, the AVP usually gives you a warning if you are too close to objects. You have to be careful. I seldom use complete immersion and find "augmented" reality more useful.
When I am using on a plane (e.g. watch movies), I avoid immersion so I can see others around me. The "movie screen" may obscure the people in front of me, but I can react to others around me. I don't think it would be a good idea to go "full immersion" in a case like this.