Retain the SEO value of the deleted page
If a link that leads to a 404 page is not redirected, eventually, it will stop being indexed by Google. This means that any SEO value that has been built up by this page will be lost.
Continue to benefit from backlinks
Backlinks are a top ranking factor for SEO. When other sites link to yours this is known as a backlink. However, if a backlink leads to a 404 page you lose the value of those backlinks.
Create a better user experience
User experience is another important factor for ranking. When a customer clicks on a link to your site and views a 404 page it can be a bad user experience. As a result, they may quickly exit the page.
Important Note: In all cases it is important to redirect to a relevant page. If Google does not consider the redirect page to be relevant they may treat the redirect as a ‘soft 404’ which can hurt your SEO.