I haven't tried it myself, but, I would assume that this sort of instruction in CLAUDE.md would indeed make it a bit more careful, to the detriment of its development velocity, which for my use-case would be bad. I generally prefer for it to experiment in many directions rapidly, and only once we have an approach that solves the problem well, to do extensive testing.

When I was younger I was sold in the idea of data driven decisions. Everything needs to be measured, otherwise you are just biased, and bias is bad. Nowadays I do still rely on data and measurements but I also have experience and taste to judge things. Answering your question, the latter.