Good question. According to the information found, it is possible that they are used to adjust the sensitivity of the left and right analogue sticks. These buttons, sometimes referred to as 'tension buttons', allow the user to adjust the strength of the analogue sticks according to their preferences. This can be useful for fine-tuning the control of the analogue sticks in certain games or for users who prefer a stiffer or softer feel when using the analogue sticks. It is also possible that these buttons have another function, such as calibrating the analogue sticks or restoring their default settings.