In Autonomous are motors running at 100% unless programmed otherwise?

With our autonomous, we had drive train run at 50% because they thought the bot was too fast and jerky. Then we kept lowering it to eventually 5% speed. Now you’d think it would be creeping but it never seemed to decrease much. Finally we just removed the:
Drive base

“When Start
motor speed %”
function and the bot still drives. So are motors set to go at 100% automatically and the “motor speed” function are to slow it down?

Can you share your code? Thanks!