That adjuster sets the preload in the balljoints. If it's not adjusted correctly, you'll have steering problems and short balljoint life.
In general, according to Dana's instructions:
Install the adjuster just enough to catch the end of the upper ball joint, i.e. leave it sticking out a quarter inch or so.
Install the lower joint and torque the nut.
Torque the adjuster to 50 lb/ft (the actual value seems to vary by manufacturer. Moog HD's go to 70lb/ft). You'll need the correct socket to do this. Napa sells them, there's another recent thread with the part number.
Install the upper balljoint nut and torque.
I have the Dana pages scanned here