Answer from cs61c-el (David Tung 16479725) for Question 3
The principal drawback of polling is that system resources have to be continually utilized to check for input from the user.  For something like the mouse, polling may be a good idea because we have no idea when the user is going to use the mouse.  But for something like disk reads, etc, it is not useful to have polling because they could potentially require a lot of bandwidth, and we are not receiving input continually.