Since the ends of your hair are the "oldest" parts of your hair, it is fragile and prone to damage and breakage. The potential damage and breakage is increased if the ends of your hair are dry. That's why anyone worth their weight on YouTube and blogosphere states that moisturizing and caring for ends is a major part of any hair care regimen.
It seems over the years, that many have abandoned this method of keeping ends moisturized. I will say it's not for everyone and you have to continue to pay close attention to how your hair responds to all-day moisture. But for me, it was a key part to my length retention while relaxed.