Building a decently sized C++ codebase takes 20 minutes. Then you want to run tests on it.
But I like to touch common headers - say to document logging macros, and printf-format annotations to catch bugs, or maybe to optimize their codegen - and those logging macros are in our PCHes for good reason - so that still means rebuilding everything frequently. Which ties up a lot of build time (30-60 minutes per config per platform, and I typically have a lot of configs and a lot of platforms!)