Sure, but when programinng, what the machine does and how long it takes, sometimes does matter. I have to think of all those jQuery examples floating about out there that just do $('#foo') in several places -- sure, it looks simpler than putting it once into a variable, but from the viewpoint of what the computer ends up doing it's utterly ass-backwards.
There's no reason a `.where` should be slower than an explicit loop though. Indeed it should offer more opportunity for future performance improvements, because it doesn't constrain the implementation with irrelevant details - the compiler is free to e.g. make the loop run backwards, or split the collection into chunks and parallelize, if it figures that that would be faster.
