Dwarf, Bushy, or bedding plants can be pinched out to generate more growing shoots & more flowers in the first year.
The taller ones should not, wait until next year when growing from a tuber, then, for larger flowers the number of shoots should be kept to 4, or for more smaller flowers, pinch out.
Pinching out should be after the second or third pair of leaves - this give 2 sets of nodal buds (buds at the same point where the leaves sprout from) a chance to sprout, incase one set fails.