Here's a page I found that explains pitch curves and throttle curves with some diagrams. Look at the throttle curve diagram, which graphs the relationship between the stick position and the throttle setting. Note that whether your transmitter has a 3 point or 5 point throttle curve, the transmitter will interpolate the rest of the curve between the points you can configure. So it's never the case that if for example you have a 100, 80, 100 throttle curve, that your throttle jumps suddenly from 100% to 80% as you move the stick. It always changes gradually according to the curve you have set. It's just that the more points on the curve you can configure, the more control you have over the shape of the curve.
http://www.swift-tuning.com/curves.php