I think the problem with yielding an array of lines is that all the code that uses the result of the function would have to be aware of this grouping of results

I think the problem with yielding an array of lines is that all the code that uses the result of the function would have to be aware of this grouping of results all the way up the stack. What he was proposing was a solution that looked like you were only returning one value per iteration (so none of the code doing the processing had to be aware there are arrays of values) but underneath the covers was actually being processed in batches on each run through the event loop. It's actually a very elegant solution. The only code that would have to be aware that it's actually dealing with batches of values is the code producing those batches right at the top of the stack of calls.