Why should you use WinMover? You probably have move and resized windows with the title bar and the borders before, which worked.

The short answer

You manage windows all the time when working with a computer. But this, the most common task, can only be performed by hitting those tiny tiny borders of the window. WinMover will make you more efficient and lower the requirements on your hand to preciesly navigate the mouse.

Why zero is better than two

Another reason is highlighted in a quote from a book by Joel Spolsky about user interface design:

As it turns out, there are lots of good reasons why you might want a window exactly at the top of the screen (it maximizes screen real estate), but there aren't any reasons to leave 2 pixels between the top of the screen and the top of the window.

[...]WinAmp has a great feature. When you start to drag the window near the edge of the screen, coming within a few pixels, it automatically snaps to the edge of the screen perfectly. Which is probably exactly what you wanted, since 0 is so much more likely than 2.

Nobody wants those two pixels, but they are all too common. Why bother wrestling with your mouse to get the window exactly where you want it? WinMover can do it for you, with any window, not just WinAmp.

If the short answer was not enough: Pixel math

The standard windows title bar is 18 pixels high. That means that to move a 800 x 800 pixels big window you have to hit a rectangle of 18 x 800. With WinMover you have the whole 800 x 800 square to hit, which is about 45 times bigger.

It gets even worse when you try to resize the window. To resize a window in two directions, you have to hit a area of 4 x 40. With WinMover, you have a area of 160 000 square pixels to hit, which is a thousand times bigger! One way is easier.