Springs on rocker shaft - Why?

[EyesWideShut]

Before firing my bike up after winter shutdown, after changing my timing belts, I started the valve adjustments and found that #4 exhaust rocker was not lined up on the top of the valve. I saw that the rocker had kicked right along the shaft compressing the shaft spring.

I never really paid attention to the shaft springs before and was wondering how the rocker had moved sideways out of position and how long had I been running it like that. I am thinking that while taking the valve cover off to do adjustments I forced it by #4 moving the rocker over. I just loosened the adjustment and repositioned and adjusted it correctly.

My question is why is the spring there? I would have thought the only movement of the rocker would be up and down pivoting on the shaft and locked in place and not held laterally just by the spring on the shaft. Why would sideways movement be allowed?

This is a double post. I mistakenly posted it earlier in the "How To" section.