I play a lot of piano and harpsichord at a very advanced level, and almost always use the sheet music. For me, it's a memory aid and a sort of "map" to the piec

I play a lot of piano and harpsichord at a very advanced level, and almost always use the sheet music. For me, it's a memory aid and a sort of "map" to the piece. You can also write stuff on your score to have reminders. This takes cognitive load off when you are performing. The goal of music is to play the music, so why waste brain capacity on getting to perfect memory of a piece when you can instead spend that on making the piece more expressive? I will also say that learning to play without looking at your hands is a great skill to have, and also takes off some of the cognitive load.