What is SOAP, Prototype, CAKEphp and why should I care. If you can do everything with a given language why all the stupid extensions?
SOAP is a standard for exchanging XML-based messages over a computer network, normally using HTTP. SOAP forms the foundation layer of the web services stack, providing a basic messaging framework that more abstract layers can build on. (copied from wikipedia) I think both, and i'm sure about CakePHP, are Application Frameworks (CakePHP is one for PHP and Prototype is one for Javascript, i think). An application framework is a set of scripts (usually OOP) who offer the functions and classes to do the stuff you do regularly on your website. Most of them include easy database connectivity, template engines, and basic form processing (checking for valid email addresses, ...) They make it easier for a developer to create a website. Usually when you create a website you have to write this stuff over and over again (or you copy it from one you allready created), but with an Application Framework you can use the built in classes, saving you a lot of coding time.
You SHOULD care about SOAP because is not a stupid extensions on a language. With SOAP and PHP you can add thousands of web pages to your site for free. You only need to find a site providing free web services (XML Data) related to your site.
The utility of SOAP will make sense if you ever do a Moderately complex MashUp or Enterprise Integration Project.