Intrygujący element na główce gitar

By feeding the strings under the string tree(s) it pulls those strings downward, creating a clearly defined pressure/fulcrum point at the nut where the string breaks over it. This helps keep the string seated in the nut and also provides a more ddefined endpoint in the string's speaking length. If you don't have enough pressure there and the srings are too flat, the worst case would be that you wouldn't be able to play it in tune because the termination of the string would be at the tuner post instead of the nut, making the scale length different on those strings and the fret placement wrong, although it's never THAT bad.

They tend to be more necessary on guitars that do not have angled headstocks and have the tuners in a 6-inline configuration as this creates a very shallow angle between the tuners at the end of the headstock and the nut, like on a fender which was designed originally in the 1940's with a flat headstock to faciliate producing the neck out of a standard sized single piece of lumber to ease production.