Tomatoes put out small branches between the existing side branches and the main stem. The plants will grow into bushes if these small extra branches are not continuously pinched off. The picture shows two spots between the main stem and the branches where extra branches have been removed. If you don’t do any pinching and the plants turn into bushes it’s likely that they will not bear many tomatoes, if any.
I only have two plants this year so it’s easy to manage. I’m wondering how this is handled in a tomato field. It seems like it would be a lot of work.