The Minimap shows the lines of a text file in miniature -- at least, as many as it can -- and shows a shaded area to represent the section of the file currently filling the edit window.
If you click on a certain line in the Minimap, one that's below the highlighted area, you'd expect Sublime Text to respond with one of two behaviors. You'd expect Sublime text either:
a) To page down one full screen (or half a screen -- some consistent amount) so the highlighted block on the Minimap moves one "step' down toward where you clicked, or
b) To page down far enough so the line you clicked on in the Minimap will be on the screen in the edit window. Preferably smack in the middle of the window.
Sublime Text doesn't actually perform either of those behaviors that would have predictable results. When you have a large file -- large enough so that not all its text will fit in the Minimap -- clicking below the highlighted area in the file does indeed jump down somewhere in the file. But it's not a short jump, and it's not to the line you clicked on. You're on some other screen of text, and you remain with the need to navigate to the spot where you wanted to go.
Currently, the only way to use the Minimap for reliable navigation is to "grab" the shaded area and move it up or down.