My wording was not precise. I should have written that available light is the most critical factor in plant growth, but certainly not the only factor. If a plant has poor or marginal light, repotting, fertilizing and watering will not make up for it. Plants in minimal but survivable light (the condition for many houseplants) will grow very slowly and rarely need to be up-potted. Up-potting such plants will not make them grow better because they are unlikely to be potbound.
Loosening the roots wrapped around the outside of the rootball will help them integrate better into the new soil. Doing it gently is the operative word.
For sure, many folks know when to repot and how to do it correctly. Unfortunately, for those with less experience it is too often done unnecessarily and incorrectly. It also seems to be viewed as a cure-all for all manner of plant problems.
