Indoor grower here, but the underlying mechanism doesn't change whether growing indoors or out.
The crown of a apex contains a majority of the plant hormone auxin, auxin is responsible for keeping a majority of the energy created kept in the central stem and will maintain apical dominance throughout its life.
When you top, you cut off the part of the plant with all the auxin, and now the plant as a response will distribute that energy far more evenly across each remaining stem. Essentially making it a free for all, all remaining stems will receive energy based on a more even distribution.
Won't technically increase yields, but what it will 100% do is encourage lateral growth, one of the most popular and encouraged genetic traits is to have quadlateral growth from each internode as opposed to the regular of two.
Total yield will be determined by many factors mostly the DLI, distribution of that energy will be dictated by hormone balance. 1 mega cola with alot of nice side cola. Or all big side cola. With increased lateral branching this can increase concentration of potential bud sites. Given its outdoors more is generally better.