Using a keyboard accelerator has the same effect as choosing a menu item. While menus provide an easy way to learn an application's command set, accelerators provide quick access to those commands.
Without accelerators, a user might generate commands by pressing the Alt key to access the menu bar, using the Arrow keys to select an item, then pressing the Enter key to choose the item. In contrast, accelerators allow the user to generate commands with a single keystroke.
Like menu items, accelerators can generate WM_COMMAND, WM_HELP, and WM_SYSCOMMAND messages. Although, normally, accelerators are used to generate existing commands as menu items, they also can send commands that have no menu-item equivalent.