The springs keep your BRIDGE in place. The bar is screwed into the bridge. On that model, if the springs are adjusted correctly, then the flat plat the bar screws into, when viewed from the side, is parallel to the strings (or to the top of the guitar, if that is flat and not an arch-top – the model shown is a flat top).
All the bar does is pivot the entire bridge on the axis provided by the two outer screws, at the edge closest to the bridge pickup (the lower one is partially hidden by the bar in the pic). The bar itself has nothing to do with how the bridge lies, the tension, or the tuning, when it’s not being actively used. The screw you’re talking about only adjusts the tension of the bar – whether it swings freely, swings with some resistance, or is held fairly solid. The bar is literally nothing more than a lever, like a prybar/crowbar. It provides leverage and feel to move the bridge on its pivot point, which raises or lowers pitch of the strings.
If the collar or bar won’t stay where you want it to, it probably needs to be replaced.
http://www.guitarpartsworldwide.com/s2g/pguitarparts/Exploded_FR_Pro.gif