@Abeserra - These buttons revert to the previous (or next) state. So, if you select “Option A” and then select “Option B”, clicking undo will reselect “Option A” (and call the appropriate callback). They are mostly useful for complex apps where people might want to go back in time through their selections (especially if they selected something unexpected).
Overtime, there might be a richer “Dash toolbar” that allows for more types of actions (saving, undo/redo, downloading), this is just the start.
You can always remove these buttons with css, see Is it possible to hide the floating toolbar?