The crimp performs two functions. The first is to remove the belling that you apply to the case to facilitate seating the bullet. If the belling isn't removed, then you will definitely have feeding problems in most pistols, since there will be a small ledge to catch on the chamber mouth, etc.
The second function is to provide an additional amount of tension, if needed. Some pistols are pretty violent in the action of stripping the round from a magazine and jamming it into the chamber. A crimp will help to prevent bullet setback, but neck tension is really more important for doing this in most calibers. There are exceptions, where the case has a very short neck. The 357 Sig and .400 Cor-Bon come to mind in this area. On the other hand, an excessive crimp can defeat neck tension and actually loosen it. You have to arrive at a happy medium, which means just removing the bell.
Since your 9mm headspaces on the case mouth, you don't want the crimp to be excessive, just enough to smooth out that portion of the case. As zxcvbob points out, most 9mm seating dies have a taper crimp built into them. Take out the seating stem and clean the die and look inside. You should be able to see the step in the wall of the die that performs the taper crimp. Some companies stamp "Taper Crimp" on the die, and some will simply stamp "TC" on the die. It's usually near the stamp identifying the caliber of the die and what it's purpose is. If your die is a TC die, then you just have to screw the die further into the press and then adjust the seating stem for the proper length of the loaded round.
Hope this helps.
Fred
