There might be numerous reasons why you need to redirect a URL. Say for example you have a broken web page that is returning a 404 error but you know you have backlinks pointing to that page, you need to show the person browsing a similar page or alternative to the content that used to be there.
In fact, fixing broken links on your website is an absolute must for SEO. Not only will fixing the broken link help with you overall SEO, you will get another backlink to your site for fixing it.