Like some electronics, this linear motion Pico servo doesn't like running at over 5V. Even slightly less is better. This adapter board adds a bit of voltage drop to a 5/6V system to make your servo happy.
The ST Micro L7805CV is a 1.5A, 5V positive linear regulator. It is the stronger older brother of the 78M05 but ironically it is the same size and shape, go figure. It may look like your everyday 7805 but looks can be deceiving!