Content Switching and Header Modification both examine the HTTP stream and make decisions based on the content therein. The result can be directing to specific servers or modifying the stream based on rules. These consume some more memory. The main drain on resources is CPU load. Depending on the quantity and complexity of rules, this can dramatically impact performance. If more than 5 rules are being applied to a service it is strongly recommended that you contact support to check if things can be simplified in some way.