But do you install additional heads when a big tree(s) block the spray from one head reaching the next head? If not, then you have not adhered to the true head-to-head philosophy of every square inch of lawn receiving water from at least two heads.
There is a point where the head-to-head philosophy could be seen as saying that you do not trust in your sprinklers to be capable of stand-alone coverage. There is enough crummy equipment out there to make that a motivation, but one should be using equipment they can trust to be effective.
Mind you, I recall the era when the finest sprinkler systems, bar none, were using brass popup sprays (mist heads, they called them) in triangular spacing of about twenty feet. Never, ever, in head-to-head spacing.
There is a parallel between recomending head-to-head spacing only, and recommending RPZ backflow prevention only. You know they'll both work, without knowing any other details.