There are reasons why pruning tomatoes is common practice by some gardeners. One reason is that pruning will hurry-up your harvest although the overall yield will be reduced.
Sometimes tomatoes will really grow like crazy and exceed the size of your growing space. In these cases you may choose to cut or snap off some suckers or branches close to the stem to keep the growth in a more vertical direction. While you're at it, it's not a bad idea to also remove all shoots on the bottom six to twelve inches from the ground. The wounds will heal naturally in a couple of days.
For tall-growing indeterminate varieties, some gardeners choose to train their tomato plants to one main stem so they don't sprawl and are easy to single-stake. I like to train my plants this way when I'm growing tomatoes in pots, or don't have room for the plant to spread out.
Cut or snap off all sideshoots other than the main stem. It's also a good idea to remove any yellow or brown branches on the lower part of the plant.
If you want to limit the height of the plant to the stake height then pinch off the top of the plant. While pruning keep in mind that you should leave enough foliage cover to protect the fruits and stem from sun damage.
Continue to train the plant this way throughout the season--it won't harm the plant, but it's best to remove the suckers early when they are just forming. As the plant matures, you can tie the plant at intervals to the single stake.