Your touchscreen effectively functions as a giant mouse by allowing you to point and click (i.e., touch). The biggest advantage of the touchscreen itself is that it allows for a faster workflow. With most software platforms, order entry is significantly more efficient and quicker with a touchscreen. In fact, these programs are designed specifically to be used with touchscreens - for example, they often include large buttons that are easily pressed. There are, however, some software programs that include small buttons and dropdown menus and function better with a traditional mouse.
There are several different types of touch technology on the market, and if you've ever used a POS system, you'll quickly notice that the screen is different than your iPhone. This is because POS systems typically use resistive technology, which basically means the monitor is covered with pressure sensitive film (Phone on the other hand respond to changes in electrical current, not pressure, which is why you can't operate your phone with gloves on).