Both of these seem like cases where you would know you're in a hot loop. I wasn't really clear in my comment that of course you should optimize loops that you know get run millions of times. I was saying: pick your tools based on the context of the code you're writing. Most simple applications involve tens or hundreds of loops that rarely iterate over more than a few values and don't get run more than once every few seconds.

single-page web app doing n times the amount of work it should be doing because components are synced over an event bus with bindings set up wrong in a way that nobody has bothered to debug