The Spline/Bezier button on the Tool Pane will toggle all the selected objects to either show their handles, or hide them. Remember, if you switch handles off, the outline will change to its automatic shape, and you may have to add some nodes in order to recover the curves. Spline mode will almost always require more nodes than Bezier.

If no objects are selected, this button also sets how your next objects will be treated, once drawn. This button also acts as a program preference, so if you choose to always work with Bezier, the next time you run the program this will determine the state in which you start.