Ask HN: Good or bad experiences with sponsored volunteer programs?

I'm curious what types of company-sponsored volunteer programs exist. I'm especially interested in what exists for tech companies. Interested in experiences with both PTV and sanctioned UTV.

What were your good and bad experiences? Would you consider this as a employment incentive?

What as a company was hardest about starting ones of these programs?

How much time does your company allow?

Also open to general thoughts on the topic :)