The toolbar gives you quick access to your applications and settings. You can delete unwanted shortcuts and add new ones by dragging a new application from the Application folder to the toolbar.
Whereas the shortcuts on your desktop are hidden behind other windows, the toolbar stays on top, so you always have access to it. You can adjust the size, flip the orientation, move it to another position and also completely hide it, depending on what is most convenient for you.
In addition of adding and removing applications, you can also change the location and size of the toolbar.