Perhaps it depends on where you’re trying to grow them and why. Are these tomatoes for home use or are you going to market them all? One reason that commercial tomato growers would prune their plants it to have more uniform fruit. Sort of like if you’re growing apples, you want only certain branches producing fruit in your trees if you want nice big apples.
If you’re growing big tomato varieties in your backyard garden, space is no where near the issue it is in a greenhouse or indoor grow space. If you’ve got a garden of goodness crammed into a 4′ x 4′ grow tent, pruning will not doubt become necessary, because a slicing tomato plant can easily reach proportions of more than 4-feet wide.
However, be forewarned that if you prune your tomato plant like a bush by topping it, the reaction will be to get bushier… probably not the right method in the indoor garden.
These plants in my garden weren’t pruned at all and are way over 3-feet wide before any fruit is ready for harvest. In a grow room, this kind of unhampered growth would choke out everything else.
Some backyard gardeners pinch off just the sucker stems that form in the crotch between an original branches and older formed growth. Now in a colder climate with a short season, this makes no sense. You want every new growth tip you can coax out of your plants to get a good harvest before frost. In places like California and Arkansas, this pruning practice makes much more sense for outdoor growing.
Here’s some professional tips on how to prune tomatoes for indoor growing.
If you don't find her at the desk - check the gardens. When not writing and weeding, she enjoys a good book, painting junk furniture, and blending the harvest of heirloom tomatoes and chiles into salsas.