Pruning of tomato plants can be overdone. If you want the largest, tastiest crops, you'll give some of the suckers a break.
Suckers are late-flowering branches formed in the leaf axils of larger stems. Removing them makes plants narrow and open, better suited to close spacing and easier to support than plants whose suckers are allowed to flourish.
And because pruned plants pour all their strength into a limited amount of growth, you get larger, earlier, more shapely tomatoes.
But you don't get as many of them, and they may not be maximally delicious, because sucker branches make lots of leaves. Good things about leaves include the energy they provide for making fruit and flavor (the more leaves in proportion to fruit, the better the fruit tastes), and the protection they offer against sunscald, which often afflicts tomatoes grown on radically pruned plants.
So unless your gardening season is very short or you have an eye on the county fair, the best resolution is compromise. Keep several of the earliest suckers, but remove those that form too late to produce fruit before frost.
The Oregon State University Extension Service recommends removing all suckers below the first flower cluster, and keeping two to five main stems. It also advises removing yellow or brown leaves and leaves that are close to or touching the ground. As a plant grows, it should be thinned so you can see into it.
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-- Homes & Gardens staff
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