What are the two taps in my kitchen ?

I know what the taps do but i have one that has the type that you pull up on the one and only handle and move it left or right for the hot and or cold temp water.. but i also have a smaller tap just beside it with a push down lever (black plastic) and cold water comes out... is this a tap for Cold water only and why would we need two taps.. rather than just using the main tap and only allowing the cold water to come out?

Thanks,

Dave