That spring pushes the rubber boot up against the clutch lever to make sure it seals against water intrusion .
It also puts a small load on the clutch arm to take up the free play from the cable adjustment, there is a small gap between the clutch pushrod and clutch arm adjustment bolt when the cable is adjusted correctly .
When removing the clutch arm at the transmission, make sure the clamp that secures the boot on the transmission case is loose, or removed and that the boot is pulled free from the case, the spring will put enough force on the boot to tear it when the pivot bolt for the clutch arm is removed, if the boot is old and hardened with age .