Surely the question is more about about a personal log?
In which case Yes - you should keep a log of all trips/experiences. It
should include miles, whether tidal or not and how many night hours and
of course from where to where and be signed off by the skipper
(yourself if you are the skipper) The purpose of the log is to
demonstrate your experience - not for any legal reasons but simply when
you come to charter or take any practical exams to show that you are a
crew/skipper of some worth. In the UK the RYA issue all our
certificates for leisure sailing and practical exams need to be backed
up by experience such as this log would show. Look at www.rya.org