When you configure buttons/selections on IF Panel, this switch prevents accidental press. - So you need to be in ACCEPT in order for button press to register. - INH prevents IF button from working.
In Aux 509, you can set this to enable/disable per individual configured button. - Have a play with it.....very effective. - Enable setting = ACCEPT required for button to operate. - Disable setting = INH/ACCEPT function not applicable.