True, but carrying does not necessarily imply using, and a proper sheath
should keep a knife blade in safe queen condition, even when carried...
Most sheaths actually cause
very visible blade scratches without any use (See this ApostleP video):
)
Or, if they don't, then they cause dulling from loose blade movement when carrying, also without any use. I would say the majority of sheaths actually cause, or at least encourage, both kinds of damage, to one degree or another... For instance, even a correctly done Kydex sheath can easily create dull spots by direct edge contact when re-sheathing (usually near the tip).
This is why scratches can't be taken lightly: If you don't keep track of them, how do you know something did not get into the sheath and is not dulling your edge? A scratch does mean something
hard is in touch with your blade...: It might now be trapped between the kydex halves, rubbing your edge apex the whole way...
Gaston