When it rains, you would be surprised at the amount of water that is gathered up by your roof. All this water needs to be funneled safely to the ground with as little damage to your home as possible, but sometimes poor planning when the house was built leaves a situation that can cause damage to the roof unnecessarily. For example, if there is water draining from a section of the roof onto another section, this will damage the roofing over time. While water splashing down might not seem that harmful, it can wear away the hardest material over time.
Sometimes you will see homes that have gutters that drain onto a different section of roof, and while this might seem less harmful, it will still do damage. The correct way for draining a roof is by having the gutter drain all the way down to the ground or into the gutter at the bottom of the roof.