On the Mac you can choose two different behaviors that happen when you click in a scrollbar. You can choose to either scroll to the next page when you click in the scrollbar, or you can choose to jump to the specific spot that is clicked. This is controlled in the System Preferences, in the "Appearance" section.

I like to have clicks in the scroll bar take me to the next page. This keeps me from sarcastically jumping all over a document. But there are times when I really do want to jump quickly without having to grab the scroll bar indicator. Turns out there's a shortcut for that.

If you hold down the Option (or Alt) key when you click in a scrollbar region, it'll reverse the "usual" behavior defined by your preference.