This means that he can remove his line and
leave without removing your line or similarly if you leave first.

Very important in tidal areas, because when another boater has to leave
early tide (4 AM) then he does not need to wake you! This boater will
recognize dipping quickly. This practice is very commonly observed in and
around the North Sea countries, where rafting and tying up 6-7 boats wide is
not uncommon!
Especially, if you have kept your mooring lines without enough slack .
Or, they may do unintentionally a sloppy job re-doing your mooring lines ;-)
--
c ya Wim
www.cork.org