My guess is that annuals can be pinched, unless they flower on the terminal growth; no need to pinch perennials except for chrysanthemums, which need to be pinched; no need to pinch woody things. If the plant is one of the last two and flowers/grows on the terminal growth, don't pinch it (think evergreens). That is my guess, as I don't pinch anything. Why do you think you should?

Need to be pinched? None that I know of!! In 50+ years of gardening, both personally and professionally and I can't recall ever pinching a plant unless it was to remove a small amount of terminal growth that was damaged or rolled to conceal an insect.

I have given various perennials the Chelsea chop, but that is much more than simply pinching and a pretty informal, rough action undertaken with shears or pruners or scissors. And is usually restricted to late bloomers that produce multiple flowering stems - asters, heleniums, perennial sunflowers, daisies and mums, upright sedums, etc. It helps keep the plant less leggy/more compact and can increase the bud points for flowering. It can also extend or delay the bloom period slightly for a longer season of interest.

It is beginning to get a little late in the season to do this now - this is typically a late May/early June activity - and could prevent flowering if done too late. Generally the end of June is the cut-off point. For example, I wouldn't do it now on monarda, which has already set buds in my area.

And you can cut back many perennials after flowering, both to renew summer stressed or tattered foliage and to encourage a rebloom, where appropriate.