95% of anything below net height will require backspin. Rafter/Sampras and some doubles specialists, past and present added a topspin volley (not of the drive variety, but a modification of a traditional, generally low, volley) that allowed them to get the ball up over the net and back down and then run away from their opponent after the bounce (into the open court usually). This was particularly useful when they needed to hit a volley with a bit of stick, but weren't in position to get their weight into the shot. It's done by leading with the tip of the racquet and hitting the ball fairly cleanly (minimal spin) and has a similar effect to hooking the ball in golf (only you have more options as far as the plane in which you do this as far as the orientation of your racquet goes in tennis). Usually, but not always, this is done from the fh wing.
Backspin can assist the volley in shooting through (skidding) after the bounce as well, esp on grass/syn grass (fast surfaces).
High volleys often don't need any spin at all as you can hit them down toward the court, so you don't need to take any pace off the shot via spin to enable it to land in. You can also hit topspin high volleys (e.g. to assist with obtaining a sharper angle on your shot, or to bring the ball down if you're not in a position to do this with the angle of you're racquet - e.g. the balls floated over your head)
The spin put on your volley should be a function of both the incoming ball and where in it's flight path you make contact with it, and what you're trying to do with your shot.
Is disguise a priority? (At times sidespin shots can assist with this as you can swing/transfer your weight in one direction and deflect the ball in another or give the impression your going to do this in order to deceive).
Taking the ball as early as possible might be key on another ball, (E.g. your opponent has floated the ball back from out of court), In which case you may make no attempt to disguise the direction of your volley, just take it as far up in the court as possible and place it to a part of the court they don't have time to cover. In which case for a high volley, you'd hit as flat as possible if it ends up being a low volley, you'd hit with slight backspin.
You need to have sound bread and butter on the volley, but there's also room for creativity, improvisation and innovation.
(So a given situation might require a response with spin on an infinite number of planes/axes of rotation) My rule of thumb is if I can win with the point stock standard volley technique I'll always do that, if not I'll try to invent something. So if the balls coming slowly I'll try to accelerate as quickly as possible toward the net with little Federer like steps, in order to use the exact same technique I do on the faster balls. It's the pace differential that's important, between the volleyer and the incoming ball.