You never have to add dry hops. It is common to add dry hops to certain styles, such as IPAs, to add hop aroma that is lost when gases escape during fermentation.
I'd recommend you take a look at this site to see the different ways hops change your beer, depending on when you add them. You can add hops at many points during the brewing process, and when you add them makes a big difference in what they do to your beer.
Read my brewing blog here! Last of the Zyme Lords
BOUSIRIS BOUERY - Home of the Zyme Lord
The cans of Leinenkugel's had masking tape on them with JOHN'S printed in ink. Amy looked around me and said, "John is protective about his beer, isn't he?"
"I put that label on there. When company comes I want them to know the Leinie's is his, not mine." - David Wong
Anna Livia Irish Stout
Melancholy Bill's Infinitely Sad Pumpkin Ale
Lucian's Landing Ginger Metheglin