Sure there are situations where you might not use the CGI module, but

• Optimizing parameter parsing is not going to give you any significant speedup unless you've got tens of thousands of parameters and hardly do anything with them.
• URL decoders are not hard to code, except that people seem to forget to implement the full spec. (See for example & vs ; separators)
• Lack of experience is not a valid reason to keep code that could be replaced with a well-tested core module.