Not sure all would agree, but the norm is to try to place a coin you take in a different cache within a couple of weeks. It's really a bad idea to grab a coin and not log that you took it. The owner will wonder what happened and there are cachers who target caches with TB's or geocoins.
If you take a TB or Geocoin, read what the owner wrote as to what the mission is. If you find a coin in Kittery, and the owner wants to see the coin travel south, don't move it to Bangor or Fort Kent.
The key is to log it promptly and not hang on to it. When I first started caching I put a lot of high end ( 15 bucks or more ) coins out and they are all missing except for one. Most were simply picked up and kept, ie stolen as I say.
To get a feel for this, you might want to put a few of your own out to see what happens. It's really fun when they go a bunch of miles, but not good when the go missing, are grabbed by a new cacher who doesn't know better, or get placed in a cache that is rarely visited or doomed to be archived.
Sometimes the road less traveled is less traveled for a reason.