What are the reasons for filing an RCE as opposed to a continuation application?

One big difference between an RCE and a continuation application is that with an RCE, your application remains with the same examiner and prosecution picks up where it left off. Filing a continuation may delay examination of your continuation application and it may be examined by a different examiner which means you may truly have to start prosecution all over again because the new/different examiner may not be up to speed on all of the issues and amendments that you already discussed and argued during the previous prosecution.

A continuation is advisable if, for some reason, you are not truly pleased with the claims you may have gotten allowed in the previous application - you can then file a continuation application before the original application issues as a patent. You may get a different examiner and therefore you may have a chance at obtaining better claims. You will have to pay maintenance fees for both patents but then again, you can elect to have the original patent lapse by not paying the first maintenance fee and maintain the second/continuation patent because the claims are better.