Sony's method of wasting a perfectly good switch on their portable players. Basically for the braindead among us, turning this switch on will prevent the volume from going above a "safe" level. This is probably the first thing people turn off upon buying a new Walkman, as it limits volume to about 50% of what the unit can put out, rendering it useless on things like buses and trains, where they are commonly used. I think Sony gets out of putting in that "We want you listening for a lifetime" booklet in exchange for this though.