if you work on a non-trivial c++ code base, being vigilant about compile times can literally make the difference between compiling your codebase from scratch in a minute vs. compiling it in an hour or more. 0% exaggeration here. With similar relative differences for incremental compiles. Nothing kills a code-base's hackability like waiting around to be able to actually run code you wrote.

Include code style is also just the tip of the iceberg. This also includes not using many c++ features that blow compile times up unless the gain from using them is so big that you eat the compile time (like containers would be an obvious example).