Practically speaking, if only one person were invisible, that person could guide the activity... (edited the helloutta that - very delicate topic, best to move on.)
If I could be invisible, I'd like to spend a day following (I'd say "shadowing" but how does an invisible person cast a shadow?

) different political figures and leaders. Might like to spend a day with Brittney, Jessica or Brangelina or TomKat - just to see how a day in their life is.