I've been led to believe there's a difference between how a MacBook and an iPhone/iPad consume power: when a MacBook with a fully charged battery is plugged in, its components draw power directly from the charger while when an iPhone/iPad with a fully charged battery is plugged in, its components still draw power from the battery which is frequently recharged to keep it at 100%. Hence, it doesn't make a difference to the battery's overall lifespan whether the iPhone/iPad is plugged in while you use the device.
Or in other words, if I'm using an iPhone/iPad and am not worried about battery life, there's no point in plugging it in anyway in the hope of prolonging battery lifespan?
Is this correct or have I been misinformed?