Answer

Why set-up 301 redirects?

301 redirects are set-up to ensure existing links, such as those held by Google and other search engines, continue to take the user to an appropriate page even though the actual page (and URL) has been removed.

For example, on this site:

http://www.zerotouch.com/style-guide/styling-of-testimonials/

was moved to:

http://www.zerotouch.com/style-guide/47/styling-testimonials

So therefore, a 301 redirect was set-up to take a user who enters (or clicks on) the first URL to the second URL.

When set-up 301 redirects?

301 redirects are typically set-up when a new site is released or the structuring of the existing site is revised.