Comment by Marazan
Because if you don't understand how a tool works you can't use the tool to it's full potential.
Imagine if you were using single layer perceptrons without understanding seperability and going "just a few more tweaks and it will approximate XOR!"
If you want a good idea of how well LLMs will work for your use case then use them. Use them in different ways, for different things.
Knowledge of backprop no matter how precise, and any convoluted 'theories' will not make you utilize LLMs any better. You'll be worse off if anything.