Pruning and "training" of tomatoes in hydro is systematically done for several reasons by commercial growers.
1. Less foliage sweats- and consumes less water (
nutrients)
2. Most of the foliage, except the parts that are close to the clusters is actually not needed by the plant (in terms of
nutrient reserves).
3. Less foliages permits better control and easier care, as well as better overview of plant ripening.
4. Pruned plants are better aerated, easier cooled and less prone to wilt, fungus and disease.
5. Pruned plants with less foliage are less heavy and need less support in the growing and blooming stage.
6. If using artificial light, it is more efficient with partially pruned foliage.
7. Most indeterminate tomato varieties get trained to only grow two branches with 4-5(+) clusters at each branch. This is what has been found to be most productive in relation to a short or medium growing period.
8. If hyperfed in a optimized green house environment they' would just sprout and expand dramatically and exponentially to some jungle, if not pruned properly and regularly. The secondary effect would be irregular sized fruits and huge variety in ripening time. Both outcomes are not wanted with commercial purposes.
PS: some varieties may require different pruning, or will even do better without any- or much pruning. Determinate tomato varieties and wild species are less often pruned, or they are trained in a different way.