Some plants have very crisp, thin stems and can be deadheaded using you fingers. This type of deadheading is referred to as pinching. Coleus plants are grown for their foliage, not their flowers. Pinching the flowers off of coleus plants encourages the plants to become bushier and fuller. Other flowers that can be pinched include daylilies and salvias.
Many fall blooming perennial flowers are pinched early in the season, to prevent the plants from becoming tall and floppy and to induce more flower buds. Pinching plants like mums and asters will also move their bloom time back a few weeks, giving you flowers in late September, when the rest of your garden is dying down,rather than in late summer.
To pinch fall bloomers, start by removing up to 1/3 of the plant when it reaches about 6" tall. Repeat that process every 2-3 weeks, until the 4th of July. Then let the plant grow and set its flower buds.