A regeneration value defines an orientation of the motion axis relative to its zero point, and actually constrains the motion axis' degrees of freedom during regeneration. When you select the Enable regeneration value check box and enter a value, the value you enter is used instead of the motion axis zero whenever the model is regenerated.

Although configured motion axes are visible in Assembly mode, you must redefine them in Mechanism Design where conflicts between different motion axes are visible. In Assembly, each motion axis is configured independently and conflicting motion limits are not visible.