If we start with the belief that volunteers can help advance our mission in important ways, then, we need to also realize that it is likely they won’t understand how to do that effectively without our guidance.
It is unwise (and will be viewed as unprofessional, btw), to invite people to volunteer and, then, also ask them how they want to help without providing some guiding framework for their volunteer work.
On the other hand, we present as competent and prepared when we provide a handful of helpful ways in which volunteers can assist the advancement of the cause. They leave the experience feeling useful and we get helpful work completed.
But, a culture of helpful volunteering begins when we hold the sincere belief that they can help advance our mission in important ways.
Without that, we are simply doing busy work.