Rough estimate, meeting humanity's energy demand (132 PWh per year - that's all energy, not just electricity), with a reasonably efficient fusion station, we'd

Rough estimate, meeting humanity's energy demand (132 PWh per year - that's all energy, not just electricity), with a reasonably efficient fusion station, we'd make 3,000-5,000 tonnes of "waste" helium per year. But as others have alluded to, it's quite a useful element and the general concern is we don't have enough.