Timing in animation is vital, it’s what most affects the believability of a piece and gives a sense of an object characteristics (eg how heavy or light an object is) or characters mood (A person blinking quickly might be seen as alert, whereas a person blinking slowly might appear tired.)
In animations the standard time in 24 frames per second, however, the amount of drawings or poses in within these frames influences the outcome a lot; more drawings between the main point of the animation mean the animation will be slower while less drawings between the point will make the animation faster.
Drawing on Ones: 1 drawing for each frame. This makes it easier for viewers to process what’s happening in each shot.
Drawing on Twos: 1 drawing for every 2 frames. This is good for faster actions and can make movements seem smoother