I'd say not only is fundamental, it's pretty much the only tool you have to start the analysis of an FP algorithm. If you want to analyze a naive sum algorithm

I'd say not only is fundamental, it's pretty much the only tool you have to start the analysis of an FP algorithm. If you want to analyze a naive sum algorithm for instance you do that by recursively applying the a ⊕ b = (a + b)(1 + ε) rule and figure out how the epsilons bubble up - the result being that the error is linear with the sum length.