Hi 
It 'shouldn't do' but what should happen and what actually happens are
often at least 2 different things. In this case it's very unlikely to go
wrong though.
The main thing is to have a duplicate 'copy' in ODF format as a back-up in
case the file does go wonky. Ideally either emailed to yourself, or copied
to a Cloud, or saved on a usb-stick or on a different machine or just
somewhere other than the 1 place you usually use it from.
I suspect that your file is of the type that it's already got several old
versions of itself floating around in different places already - and that
might be enough if the main up-to-date version ever does go wonky.
Between LibreOffice 3.x.x and 4.0.0 there were significant changes that
made it worth refreshing quite a lot of documents in the way you
suggested. Ideally pasting as unformatted text or by going via a
text-editor to strip out all the cruft defunct formatting accumulated over
the years - and then reapplying styles and formatting after.
I don't think it's been needed since then.
If you bounce it around between different formats, especially if it's been
saved and re-used from a Microsoft format for MS Office 2010 or more recent
then it might well be a good idea to de-cruft it - but that is more to do
with the messiness and constantly changing "transitional" versions of it's
format used in different versions of MS Office.
If it's stayed as an Odt (or whatever) then the build-up of cruft is
unlikely to be noticeable.
Regards from
a Tom 