It is necessary to install gutters.
A professional can assist you to determine how large gutters are required for your house. However, the speaker in the video, who’s such an expert, states that most homes take 5-inch gutters. A 6-inch gutter is not recommended to be installed in a house that’s designed for a 5-inch gutter. It is possible that the bigger gutter could result in damage to the wood panel. A bigger gutter is able to hold larger amounts of rainwater, as well as debris. The added load will be too heavy for the wood. It is possible to be at risk even if your gutter is cleaned regularly. The impact of a storm is enough to cause damage.
There is no real advantage of installing a 6 inch gutter however, you must never install one when, at the top of the house you have 3 inches between an edge of the shingle towards the front of the gutter. The gutter you are installing now has all details needed to figure out which size gutter you should choose to install.