Except its utterly unusable because if you release the keyboard key and the mouse button in the wrong order, and you will, then you get stuck in the new mode.
ie. im in rotate mode. I want to quickly move something, so I hold down the E key to temporarily enter move mode. Click and drag to start moving. When you are finished, you release the mouse and keyboard buttons. However, if the keyboard key releases a millisecond before the mouse button, you are now stuck in the new mode.
Or if you have a heavy scene, you press and hold E to move something, then click and drag. If c4d hasnt updated to the new tool before you click, you will be stuck rotating the object instead of moving it.