The Blend Tool

Very few things in Adobe Illustrator can speed up your process quite like the Blend tool. You need 50 circles? Make two circles with the Ellipse tool and then, blend 48 steps between. They'll all be the same and evenly spaced. Need them to change color or transition from one size/shape to another -- Blend tool. It can allow for opacity, color, shape, effect edits transition smoothly or in steps/distance to another shape with same or different opacity, color, shape... Very powerful tool.