title_body: Is it good to have the "floating oil" on the surface of some coffee drinks?
upvoted_answer: Nice question. A similar myth has been arisen for Turkish coffee pot; such as it should be cleaned only with water to keep the greasy surface made with coffee oil.
  
  Partly correct, partly not. According to my "Barista's manual" from Lavazza, this sedimented oil may acetify. Thus, end up bad flavor.
  
  Again, (I cannot remember the source) as of my knowledge, paper filters are very good filtering everything; including those valuable oils. (That's why classical French press is still very common to prepare filter coffee, I think.) Paper soak in most of the flavor itself if it does not have proper fibers. This seems like the main problem of any drip coffee machine, V60, Chemex, etc.
  
  Final words: keep it clean in the long run. You may not necessarily clean it until acetifying; which is you may keep it as it is up to one-two days.
  
  Same rule for Turkish coffee pots. :)