If you’re a regular user of Flash, you will be frequently using all the tools in the toolbar. It is sometimes very time consuming and annoying if you have to constantly switch between two or more different tools, or if you constantly go into the menu structure to select a function.
The shortcut keys can improve the usability by providing specific keys on the keyboard which link to the tools and functions used in Flash. It is often much faster to use the shortcut keys rather than the interacting with the mouse on the interface.
The shortcut keys I use the most in my projects are: F5 (Add frame), F6 (Add key frame), F8 (Convert to symbol) and Ctrl + Enter (Test movie). These particularly shortcuts can save you a lot of time, especially if you use them repeatedly. It is good to memorise the shortcut keys you use the most often, as it will allow you to use the Flash program much faster and easier.
A list of the all the Flash shortcuts can be found here: http://kb2.adobe.com/cps/121/tn_12105.html. These shortcuts apply to both Windows and Mac machines. You can also customise the keyboard shortcuts to your own preference by selecting Edit > Keyboard.