"erase" vs "clear" question

[Ruslan Nabioullin]

What exactly is the difference between the functions "erase" and 
"clear"?  From what I understand, they both have the same effective 
expungement result but the latter in addition repaints the window.  I 
don't see the point of having both available---in what situations would 
it be more apt to use one over the other?

-Ruslan