[tshaddox]

It's hard to argue with a rule of thumb that broad, but I think it's too broad to be useful in practice. You will still always need to make case-by-case decisions at your own discretion, and the rule of thumb will be unnecessary in uncontroversial cases (you probably won't even consider writing your own code to format a number as a string on your website) and will easily be ignored in other cases ("yes, we could just build our homepage and merch page in Squarespace, but we're going to want total control over that entire product so we're going to build it ourselves").