Redirects are used whenever the content of a website is given a new address (URL). This can be the case when a website is restructured or the change to a new CMS is prepared.
Redirects direct visitors to a website who arrive at a website via an old, now invalid address to the current, valid address. But not only do visitors not end up on an error page when they call up an old, now invalid URL but search engines are also informed in this way that the content has been moved to a new address. Redirects are also important in connection with search engine optimization. With their help, the search engine learns about the new address, and a good position of the address in the search engine results list (SERP) is not lost, only to be reworked again afterward.
This is what google explains about the creation of redirects: https://support.google.com/webmasters/answer/93633?hl=de