My understanding was that NoImplicitAny changes the rules of the language, so its use will make it harder to move code from projects that rely on it to projects

My understanding was that NoImplicitAny changes the rules of the language, so its use will make it harder to move code from projects that rely on it to projects that don't. Traditional compilers opt for a rich set of warnings and the ability to turn any warning into error. On closer inspection, it seems that code developed with NoImplicityAny should work 100% on projects without that, so my concern was unwarranted.