Speaking URLs" are web page addresses that do not consist of combinations of numbers and characters (for example www.ihrewebsite.ch/?id=3453), but consist of content-specific keywords.
Speaking URLs" are advantageous for the placement in the search results, because they already contain the relevant keywords in the address.
This also has decisive advantages for offline advertising media. An imprint in the flyer with "www.ihrewebsite.ch/kontakt" is much easier to comprehend and remember than "www.ihrwebsite.ch/?id=3453„.
In the case of a changeover, the old URLs should definitely be redirected to the new ones with a 301 redirect. Otherwise the damage of a change can be greater than the benefit.