Should I deadhead clematis or leave the fluffy seedheads?

Becca Skelhorn, by email

ABOB SAYS Deadheading before seeds form almost always improves flowering the next year, as it preserves resources that would have been expended on making seeds. However, the fluffy seedheads can be attractive, and those of early-flowering types are used by birds to line their nests, so I think it’s best to leave them.