Here are two examples of curves that ignore input.
IGNORE BOTTOM - ignores the lower end of logical pressure
IGNORE TOP - ignores the upper end of logical pressure
IGNORE BOTTOM
Effectively this increases the perceived IAF of the pen.
This is useful in several cases:
Your pen might be drawing while hovering and this is one way that might help that problem
Some people don't want the pen to draw when in contact with the tablet, the only want to use it to point. They can ignore pressure to help make this happen.
IGNORE TOP
Some people have issues with their hands and with pens that have a very high pressure range they can never get to the full maximum pressure. They can use IGNORE TOP to effectively lower the maximum physical pressure.