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Distinctive. Easing functions usually force the beginning and end to be noticeably different, and throughout the middle portion they're basically identical to constant velocity. The discontinuity at the start and stop are what easing functions are most concerned with.

In the limit, constant velocity still has the same discontinuity (infinite acceleration) at those points, and easing functions generally stick with the same constant-ish acceleration at those points. Easing makes it feel like the object has to get up to speed, and it takes about the same amount of time regardless of distance/overall time.