You might think that Google and the other search engines would just follow the redirects, but that’s where things get complicated. Use the wrong type of redirects, and the search engines’ view of your website can get mixed up, badly.
Many webmasters don’t understand the different between a 301 and 302 redirect. Unlike users operating browsers, search engines sense the different types of redirects, and handle them differently. A 301 redirect means that the page has moved to a new location, permanently. A 302 redirect means that the move is temporary. Search engines need to figure out whether to keep the old page, or replace it with the one found at the new location. If the wrong type of redirect has been set up, search engines may become confused, resulting in a loss of traffic.
Google recognizes that many people use 302 when they really mean 301. Fortunately, Google isn’t bound by any law to take people literally. For the sake of producing the best possible search results, Google can and should look at 302s and figure out if the webmaster really means 302, or if it’s run-of-the-mill confusion and they really mean 301.
Whether Google actually handles 302s properly is an open question. If a 302 is used instead of a 301, search engines might continue to index the old URL, and disregard the new one as a duplicate. Link popularity might be divided between the two urls, hurting search rankings. Search engines might figure out how to handle the 302, or they might not. Google spokespeople have said that they will treat a 302 as a 301 if they think the webmaster has made an error, but why take a chance, and what about other search engines?
When permanently moving a web site, or a web page, best practice is to use a 301 redirect. 302s in this situation seem incorrect. By saying “temporary move” a 302 tells search engines to keep the old domain or page indexed, but it would be desireable for them to index the new location. In the past people have used 302 redirects in an effort to circumvent the Google aging delay. This workaround might have worked at some point, but it is not a current best practice.
If concerned about losing rankings due to a 301, the solution is not to change a domain, and not to become financially reliant on rankings. In the real world, businesses avoid changing their names because it can appear shady. Who can blame Google for employing the same logic: if you’re changing domain names, you might be up to no good. Let’s wait a while and see if you behave yourself before we recommend you