Joomla 3.8 makes hidden preparations for the future upgrade to Joomla 4.
Former upgrades sometimes were hard work (remember the upgrade from Joomla 1.5 to 2.5) - so this is a relief for all website administrators.
More visible is the possibility to change the automatically produced urls, for example the url of this news: Before it contained automatically the ID number of the article. Now it is possible, to remove this. And this will be honoured by the search engines.
Some security issues are also worked on by this update.