Springs are perhaps one of the most underrated components of any semi-automatic firearm. Repeated compression and decompression will weaken a spring and eventually lead to breakage. Basically, the more rounds put through your firearm, the greater the chance a spring will break.
Like any spring, the G3 buffer spring is designed to store (when compressed) and release (during decompression) energy. In the case of the buffer spring, this energy is the direct result of an impact from the bolt. Designed to absorb and release the energy created by the action, the buffer spring is one of the most important springs in the G3.
For $3.95, you can be prepared with an original Heckler & Koch part if you ever happen to fire the fatal round that destroys your buffer spring.