I use a numpad on the left a lot. I actually use both of them ;_;
Got used to it from working/modelling in Blender, where a lot of nice things are bound to the numpad (navigation, object focusing, etc), while main shortcuts populate the left/middle side of the keyboard.
Numpad on the left is great when you're right handed and use the mouse a lot, then you have a lot more buttons in the immediate reach of your left hand, even though it's pinky-side.
Numpad on the right is good as well, because you have easy access to it with the thumb of the mouse hand. This way you can cover 100% of the numpad with minimum movement, divided between both hands
Though in general, I think there are no good fast workflows for mouse/keyboard setups :/