A guitar armrest is a protection and freedom for the soundboard and comfort playing for the guitarist.
The armrest is only attached to the very edge of the soundboard. You can see in the photo below that the armrest does not come into contact with the soundboard over its entire surface, meaning it does not interfere with its sound.
What is the purpose of an armrest:
Freedom for the soundboard. The guitarist's hand does not touch the soundboard while playing, thus not restrain its vibrations.
Cleanliness of the soundboard. Aesthetics of the appearance. The guitarist's hand constantly rubs, warms, and moistens this part of the guitar. Sweat can penetrate under the lacquer. The different layers of the soundboard and the edge of the guitar react differently to the heat of the hand. The lacquer wears down from friction. Micro-cracks can appear in the lacquer, accelerating the aging process. Some dirt may begin to accumulate at the edge of the soundboard.
Сomfortable playing guitar. The relatively sharp edge of the guitar presses into the guitarist's hand, constricting blood flow. An armrest made by Mykola Roodenko has a comfortable radius that solves this problem. Reducing pressure on the hand reduces friction, making playing easier. The hand does not catch on the edge when you need to quickly move it during the performance.