Emrys wrote:
Presumably the 'stopping' of a plant ensures that its energies are
concentrated on the production of flowers/fruit or side growths, as is
the case with tomatoes.

Plant growth, including flowering and fruiting is regulated by
hormones present within the plant. Some encourage growth while others
impede development. There's a constant and intricate interplay of
growth enhancers and growth repressants, which coordinate the plant's
development. Apical dominance, (the condition whereby a growing shoot
does not branch unless 'pinched-out') is the result of auxins in the
bud tip. These ensure that lateral buds do not commence growth too
soon and crowd out the growing tip. By pinching out the tip, the
auxins are removed and lateral buds can start to grow.

Similarly, auxins are sometimes present at the extreme tips of flower
racemes (spikes) especially In plants that open their flowers
successionally. The development of the buds is affected by the
concentration of auxins, those closest to the source being more
heavily repressed than those furthest away. As the flower spike
elongates, the distance between the older buds and the auxin laden tip
increases, enabling them to expand and open. The removal of the auxin
laden tip can cause all remaining buds to open more or less
simultaneously. Hope that makes sense.