The button on the AutoUpdate toolbar allows you to Pause Auto Update/Recalculation operations. This is a global setting in the project, so any analysis that is set to auto update will first check the property of this button. If these operations are paused, the toolbar button will look like this and the Recalculate button on the Standard toolbar will be grayed-out . Thus, even if Recalculate Mode is set to Auto for a particular analysis, auto update will not occur until the Pause Auto Update/Recalculation button is clicked again.
Since constant recalculation and auto-updating of results can slow your work, you may want to Pause Auto Update/Recalculation when your project contains many such operations.