It depends on the stage of development. Starter tree from nursery often require thickening of the trunk, development of nebari and increase in the foliage. Under these circumstances repotting to smaller pots is counter productive. If the tree has the size, foliage for styling then it is a decision based on what stage of development exists in the nebari and root ball.
Keep in mind that professionals do not go the the local landscape nursery for material to style. They are almost always working on material that has been adapted already for Bonsai ( collected) or material that was raised for bonsai purposes. In these cases the root ball is generally advanced, nebari present and the trunk already the size desired.
My preference changes on the basis of the situation. For yamadori that have recovered from collection and have sufficient foliage it can go either way! For nursery stock from a regular landscape nursery, I always work the roots first and begin development to a Bonsai suitable root ball. This may involve a smaller container but often not, they almost always need further development first.