This feature is hugely helpful when drawing anything.
Will allow coverage of a canvas with (1,2 or 3 point) perspective guidelines, easily moved and adjusted.
The artist can choose whether the lines he/she draws will snap to the vanishing points or not.
Also of help is the clear delineation of the eyeline or horizon, a problem that catches some Carderites painting a still life.
I have just downloaded the perspective function for $2.99 and had a play with it. I can really see perspective assist helping me with figure drawing.
Take a look at this video on YouTube: