Kinetin, 6-bap, 2,4-dichloro phenoxyacetic acid, and gibberillic acids can have foliar reduction effects. Or kill your plants and/or block auxin responsiveness.
They - except GA's - are known as cytokinins, although 2,4-D is debated since it can act as an auxin. The latter was used in Agent Orange as a defoliant.
The foliage size reduces because energy is distributed more easily and "strong" limbs are more or less silenced. Their effects in general are: promote adventitious growth, suppress auxin, and promote callus formation on wounds.
GA is cool on its own, it's generally a dormancy breaker but it can have long lasting dwarfing effects on some plants.
At some point though, there are going to be sports; branches that ignore the hormonal change and revert back to normal.
These chemicals are cheap. But they can have varying effects depending on the susceptible pathways and genetic makeup. So use them with caution. It's not uncommon that too high doses can stall growth for quite some time or lead to deformations.