Many flowers may benefit from some pinching of the tips - all depends on if they grow from the root ball base of the plant or from a central stem. But it sure isn't required - pinching back is optional at best and is done for plant appearance purposes, not plant health.

Very few, if any, vegetable seedlings require or benefit from pinching and some are badly damaged or killed by doing it. Onions is the only exception that comes to mind as trimming green leaves a couple of times before transplanting is beneficial.

With most other vegetables, if they get too tall and/or leggy before transplanting it is usually because they aren't getting nearly enough light.

Dave

Growanything,
Check out this link

http://www.centertonnursery.com/howto/BlewLabelGuide.pdf

Jim

That's a great resource Jim! Thanks for posting it. I especially like the opening sentence:

Now hear this. Pinching and cutting cause more problems than they fix.

Dave

Here is a link that might be useful: PINCHING OF PERENNIALS THROUGH THE SEASONS