They allow for a company to still have online exposure even if a page is broken, inactive, or under maintenance so customers AND search engines are directed to the updated content.
You can improve your SEO by writing and posting about your products often.
Redirects greatly improve SEO if they're done correctly and redirect a page to a completely new URL without losing rankings or domain authority. Poorly implemented redirects can result in a loss of organic traffic or rankings.
In order for site migrations or website redesigns to run smoothly, all previous pages need to be directed to the new location. If not, important pages may not be found.
You don't want your pages to get lost.