When moving pages to a new URL it is quite common to lose out on a lot of valuable search
engine traffic due to incorrectly configured (or missing) redirects.
It is very import that when a search engine comes to crawl
your website it is able to follow any redirects you have
set up.
Suppose you have a website http://www.foo.com and you create
a redirect such that whenever any visitor types in the URL
http://www.a1.com he is automatically redirected to http://www.a1.com/widgets/,
If the Search Engine is not able to follow the redirect
it would think that http://www.a1.com has NO contents, http://www.a1.com
would end up ranking very badly in search engines.