''From TheHumaneInterface:''

'''Modes are bad''' because they cause errors, even when there is an indicator for the mode. That's because people will focus on the task, not on indicators. This applies also for hardware (power switches are bad) and applications (restarting an application should put you back where you left it, not in another mode).

'''QuasiMode''''''s are good''' -- holding down a key to activate a mode (such as Shift, Control, Alt, or Meta) is good, because the touch required provides feedback on the mode.  Thus, LeapMode is good. So is DragAndDrop.

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Actually, to a large degree, QuasiModes annoy me.  They use up one hand and so using more than one QuasiMode is a pain.