Often the lazy pattern for evaluating iterators has bad "mechanical sympathy" and the strategy of "evaluate step 1, write it into a list" and so forth often beats the "step 1 calls step 2 calls step 3..." pattern by an order of magnitude in performance.

You just win so much by keeping the inner loop in the I-cache, having the branch predictor completely focused on one inner loop at a time, etc. Writing/reading the array burns memory bandwidth but the CPU usually likes the access pattern.

True the eager approach can fail terribly if the array is huge and it's particularly obnoxious if you are running 10^6 calculations and just one of them makes a big array, but the lazy approach is one of those lower teachings that gets passed off as a higher teaching.