Consider the foxglove a biennial. You want it to go to seed, since they form a rosette the first year and bloom the second. Therefore, don't deadhead it. If you let the seeds resow from this year's bloom, you may not have any blooming the next year, but you will have perpetuated the line and you'll get bloom the next. That's why I let my foxglove form a little colony, as there may be some in rosette form and some in bloom mode and I'll always have some bloom each year.

Peonies are true perennials and as long as I have gardened, don't ever remember seeing any volunteers come from peony seed, though it is theoretically possible. So, it doesn't make any difference what you do to the flower heads after they bloom, as far as them coming back the next year. They'll come back up from the eyes on the tubers. People deadhead certain perennials because they can rebloom the same season if cut back. Some veronicas will. Peonies won't. Others deadhead perennials for appearance sake. In an established peony plant the energy you 'send to the roots' would be negligible, but I have no idea how large your peonies were or if they're struggling and need all the help they can get. It won't hurt anything if you want to cut off the dead blooms.

BTW, peonies resent transplanting. They may not bloom again for a year or two or five. LOL.

Deadheading is more an issue with annuals, some of which want to croak after they bloom unless deadheaded.

Hmm, not referring to foxgloves or peonies in particular, but deadheading is an important technique for many perennials for a later flush of bloom (many salvias) or to prevent a blue million seedlings (Achilleas, Rose campion, etc.)

Definately........I mentioned that. " People deadhead certain perennials because they can rebloom the same season if cut back. Some veronicas will. " My Becky daisies, Sunny Border Blue Veronica are ones I see coming again the same season.

Very good point about removing seeds one might find aggressive like rose campion.