Budget Watch Collecting/Shock Protection
The balance of a watch needs thin delicate pivots and fragile jewels to run well. The balance is generally one of the largest and heaviest jewelled wheels in the watch, and thus one of the most likely to be damaged if the watch is dropped or bumped.
Shock Springs 
Modern shock protection began commercially with the introduction of the wikipedia:Incabloc system in the 1930s, although not widely used until the 50's.
In this system the balance jewels are spring-mounted, and the balance staff is specifically shaped. In the event of a shock, the balance can push the jewels out of position temporarily. If the shock is severe, a thicker and stronger portion of the balance staff will contact a strong part of the jewel setting before the jewel reaches the end of its travel. After the shock, the springs force the jewels back to their proper place. The same basic system is also used by Kif, Seiko's Diashock and Citizen's Parashock.
Other systems 
Wyler had the Incaflex system as an alternative to shock springs. In this system, the rim of the balance is connected to the staff with springy spiral arms.
Under a shock, the heavy rim of the balance would displace and contact a rim around the circumference before enough force was applied to damage the staff or jewels. (Note the cap jewel with no shock spring)
Timex used the V-Conic system. Instead of the traditional arrangement of slender pivots, Timex used a conical profile. Instead of jewel bearings, they used metal cups shaped to match the V-conic pivots. This system was both less expensive to manufacture, but also inherently stronger than traditional pivots, allowing Timex to meet shock-resistance standards with no springs.
Other wheel springs 
Sometimes you may see what appear to be shock springs on other wheels--These are actually retaining springs rather than shock springs, to allow the cap jewels to be more easily removed for cleaning. Seiko calls their version Diafix rather than Diashock.