Cut down white foxgloves or leave to seed?

[ClaudiaNaughton]

They are nearly over with flowers only on top third. Chop or leave? Does lilac need deadheading?

Chop and they will probably flower again from the side shoots. Leave them to seed. Don't know about the lilac, sorry.

I have a lilac tree in my new house and I am planning to deadhead the bits I can reach because otherwise they will just hang around looking brown. AFAIK there isn't any other benefit.

With the foxgloves I would probably hedge my bets and leave a few because I wouldn't want to risk them not reseeding.