How private should home be?

My housemates, perhaps obviously, have keys to my home. Clearly I trust them not to walk off with my laptop while I'm out. So why don't my best friends also have keys?

Even though it's unusual, it makes a lot of sense. With a key to my place, a friend can

  • wait inside when they arrive before I do
  • leave their bike at my place when they are headed to an event nearby
  • stop in to use the bathroom and see if anyone's around
  • use my living room as an "office" when I'm not around during the day

In the past this has been a bit of a hassle because keys need to be duplicated, and it's very hard to revoke access. But with an internet-connected lock, this becomes far easier, not to mention trivial to log every access.