When the egg controls are set to hasty, you can quickly tap and release A to do eggshots that will always have an identical angle every time. There is a 9 frame window, from pressing A to releasing it, for this to work. This is very useful because it allows certain difficult eggshots to be made consistent. By constrast, if egg controls are set to patient, there is a one frame window to do any eggshot with an identical angle. Because of this, for a category like 100% where consistent eggshots are incredibly important, it is highly recommended that you play on hasty.
Rising and Falling Neutral
The following gif demonstrates this concept with neutral eggshots. Watch where the eggs exit the screen on the right based on yoshi's jumping.
Upwards EggshotStraight up-shot: To do a completely vertical up-shot you have to stand still and: A) Tap A and hold up for less than 10 frames or B) Wait until your cursor is out before releasing A.
Angled up-shot: This happens when you make an up-shot by tapping A and holding up for longer than 10 frames, it's inevitable when running and shooting upwards. This also makes Yoshi face the opposite direction.