When editing a complex curve is very annoying to have all handles at a time. Also, this is a requirement for the current GSoC Edit Grease Pencil using curves.
I have seen that this improvement can be used in any other area of blender, so I have decided to publish the option in the overlay panel..
Reviewed By: fclem, #user_interface, billreynish, Severin
Differential Revision: https://developer.blender.org/D7754