Posted: 24/07/2014 at 08:32
I have pondered this question also and last year, mainly down to motivational issues on my own part, I more or less stopped deadheading dahlias, cosmos, coreopsis, gaillardias, scabious and the like. They do carry on throwing up flowers, but I think they do appear to run out of steam earlier. More important they started to look very untidy and the flowers , fewer in number, got lost among a crowd of untidy dead flowers. Some seed heads are attractive, many are not. The effect was pretty poor, so I am being more diligent this year and, more important, enjoying it.
Can't comment specifically on candytuft, but next year you could do half and half to see what happens. My guess is that it probably doesn't make a deal of difference.
Not sure if this actually answers your question, but if in doubt cut it out, or off