The Fast Entities Input button allows you to use one and the same entity several times without the necessity to activate this entity every time.
Quick Access Panel: 
Ribbon: Editor -> Draw -> Fast Entities Input
Menu: Draw -> Fast Entities Input
Use the key Esc or the command Cancel in the context menu to deactivate the current entity while Fast Entities Input mode is on.
For example: you need to draw several Polylines.
If the Fast Entities Input mode is off you will have to click the Polyline icon 
to activate it every time you wish to draw a new polyline.
If the Fast Entities Input mode is on you will be able to activate the Polyline icon once and draw as many polylines as you need until you press Esc to deactivate the Polyline entity or press the icon of another entity.
The feature also affects the selection of entities and the nature of some modifying instruments. With the Fast Entities Input mode on successive clicking on the elements of the drawing selects several entities. When the mode is off you can hold the key Shift pressed to fulfill the same operation.
While modifying elements of the drawing with the help of the instruments Move, Rotate, Scale and Mirror a copy of the selected object with some new parameters is created. The initial object stays untouched.
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