There is a familiar question among gardeners as to whether or not you should or should not prune you garden tomato plants. The fact is that tomatoes don't really need to be pruned; it is more of a choice of preference and choice to the individual gardener him/herself.
Most gardeners that do prune simply just pinch off the side shoots (suckers) of the plant depending on what type of tomato that they are growing. Pruning is basically and simply thinning the plant to prevent its becoming too top heavy, causing leaning and often splitting of the plant when they have grown out of control.
Indeterminate tomato plants such as "Beefsteak", "Big Boy", "Brandywine" and early producing plants like "Early Girl" and "Celebrity" will generally die back before the end of the growing season because they produce earlier which is why they are often called semi-determinate varieties of tomatoes. Some indeterminate tomato plants depending on their growth habit will continue to grow and produce tomatoes all season long. Pruning you tomatoes will compact them, however it will also give you a smaller yield in fruit so if the stems are good and strong leaving some "suckers" on the plant will improve the crop, giving you more tomatoes to look forward to.
If you want to prune, prune out the suckers below the first flowers stems. Many gardeners say that this method improves and helps develop a stronger central stem while others choose to leave the suckers on the lower portion of the plant because they are easily staked.
Determinate tomato plants really don't need to be pruned at all. They are a more compact growing variety of plant that reaches a certain height and generally Stop Growing. When their branches are nearly fully grown the will start to produce their fruit, usually all at once. They will not keep re-producing so pruning is not necessary. These varieties include "Rutgers", "Marglobe" and some varieties of "Celebrity". Sometimes called bush tomatoes they are generally smaller than indeterminate tomatoes and are perfect if you want a large crop at one time.
Whether or not to prune or not to prune your plants is still a matter of preference and a personal decision and depending on your garden size. If you do decide to prune, Less is "better" for the plant; to get a feel of how well it will or will not respond. Pruning really is just an experiment of trial and error on the part of the growers to see what works, what works best and what doesn't work at all.
Eudora DeWynter offers tips on Should You Prune Your Tomatoes on her blog at http://www.gardentoolguru.com