A POS system that lets you input customer names so you can track their orders is WAY cool! If they are willing to, we add their birthday to their profile and send them a gift card and other specials. It makes it possible to not force customers to carry around another loyalty/frequent buyer card since we track it for them.
From the management side: looking at our sales mix is so easy in the POS system. Yes, it's easy to know what your top and bottom 20% sale items are. Any of our employees can do that. When deciding how to restructure menu items and menu design to highlight certain items and categories, knowing what to do with that middle 60% becomes tricky. Being able to do all this in the POS system rather than bringing QuickBooks into play is nice.
I have a huge list of ways a POS system is a worthwhile thing to have, but I worked in the POS industry for years, so I have a certain bias.
Coffee Shop Manager. Google it, we've been using it for eight years in four shops. Love it.
Also, search BE as this topic has been covered a dozen times and there are many helpful posts.