I believe the RoI on best practices is generally correlated to the scale of the application and engineering team you are working on.
A large number of best practices come from Big Corp engineers or organizations. Big corps have thousands of engineers that need to be able to read and contribute to code from many other teams. They have systems that need to be able to handle millions or billions of users.
In situations of massive scale strictly adhering to best practices is worth the investment, since it will make code easier to contribute to (readability/architecture standards), make sure it does what it's supposed to (unit tests), or keeps things performant. But the RoI of following best practices decreases as you move down the spectrum of scale
A large number of best practices come from Big Corp engineers or organizations. Big corps have thousands of engineers that need to be able to read and contribute to code from many other teams. They have systems that need to be able to handle millions or billions of users.
In situations of massive scale strictly adhering to best practices is worth the investment, since it will make code easier to contribute to (readability/architecture standards), make sure it does what it's supposed to (unit tests), or keeps things performant. But the RoI of following best practices decreases as you move down the spectrum of scale