What is the purpose of the regeneration effect on a permanent?

The purpose of the regeneration effect on a permanent is to protect the permanent from being destroyed. When a permanent is regenerated, it is essentially given a form of resilience against destruction. This effect does not prevent all damage to the permanent; it allows it to survive effects that would typically destroy it, such as lethal damage or effects that say "destroy" (like the spell Doom Blade). Specifically, regeneration creates a replacement effect; if the permanent would be destroyed, it is instead removed from the battlefield and then returned to the battlefield, typically tapped and removed from any damage.

This means that while the permanent can still receive damage, the regeneration effect ensures that it won’t leave the battlefield due to destruction. Thus, the primary function of regeneration is to offer a protective mechanism against destruction rather than to fulfill other roles like entering the battlefield or creating tokens.