This post describes how to spot a Sitecore solution has become a victim of the Habitat Cargo Cult , as well as tips to prevent it from occurring. It's part of a series documenting Helix Smells - some of the common pitfalls of Sitecore development when following the Helix architecture.
Sitecore recommends caching the HTML of renderings wherever it's practical to do so. Here's a quick SQL script to find View Renderings and Controller Renderings that are not marked as cacheable.