The Style Guide currently says:

  Implement classes as if expecting rough usage by clients. Check for
  incorrect usage of a class
  using `assert(...)`, `guarantee(...)`, `ShouldNotReachHere()` and
  comments wherever needed. Performance is almost never a reason to
  omit asserts.

The Compiler team made an effort to replace ShouldNotReachHere() with fatal("descriptive message"), which gives useful information without needing to look at a backtrace. Maybe there should be common guidance about this. Perhaps deprecate ShouldNotReachHere in favor of something more informative. Or perhaps ShouldNotReachHere should take message arguments.