The benefit of fast play is that you'll get players to commit their chips with relatively weak hands since it will be hard for them to believe that you have a strong hand every single time. The downside is that your opponents will raise weak when you have nothing at all, forcing you to fold.
Some players like to add a little more spice to their no-limit Hold 'em game. They add a live blind, also known as a straddle, where the player to the left of the big blind voluntarily puts up twice the big blind before looking at his hole cards. The player in the straddle then has the option to raise it up when the action returns to him.