You have to realize that most of the information out there on the best way to grow tomatoes is aimed at commercial operations, and that information is then co-opted for gardeners, often without taking into consideration that the aims of the two growers is very different.
Studies have shown (Purdue Univ 2003, 2004, I think) that a certain amount of pruning will give a relatively small increase in fruit size and fruit quality (perfectly shaped shaped fruits), enough to increase commercial profits because fruit is graded based on size, but pruning will also decrease the overall amount of fruit produced (so you have to balance increased quality with decreased production to maximize profit). This result was found to be true on most but not all of the handful of round red commercial hybrid varieties they tested.
Are you growing for market? Will you have to throw away any undersized or misshapen fruits? If so you might want to consider pruning to 4 stems, ...if you are growing a hybrid variety bred for consistent fruit size and shape. Many heirlooms are known for being quite variability in fruit size and shape so pruning probably wouldn't make anything noticably better for you.
Other pruning methods (severe sucker pruning) are used by commercial greenhouse growers who have 20 ft tall, 2 year old plants hanging from strings. The stings are periodically let out to lower the top of the plants so that the fruit can be picked. Plants are rooted in hydroponic bags every 12 inches. The pruning makes for consistent fruit production per growth rate of the single vine. If they let suckers grow and set fruit it would affect timing of fruit ripening in relation to plant height.
If you are growing on stakes you generally have to limit the plant to 2-4 stems, so you have to get rid of the extra suckers. you can get rid of them all the way, or pinch them off above the first set of leaves (Missouri Pruning) so that the plant gets the benefit of the extra leaves to provide energy for the plant and shade the developing fruit.
So you can see that when people are told to prune there is usually a practical purpose for it, but only for a certain situation, but that situation is hardly ever specified, and usually not applicable to the home gardener.
A much more intuitive way to ensure larger better tasting fruit is to remove any catfaced (severely deformed) fruit while they are still small and green, and to limit your trusses to an average number of fruit (some varieties of tennis ball sized tomatoes normally have trussses of 5-6-7 fruits). You might want to snip off any newly developing fruit at the end of the truss that start to form after those first 6 or 7 start getting large. For a large beefsteak variety you might want to limit a truss to 4 large fruit. Another time to consider some type of pruning is about 2 months before your last frost date. Pinch off all trusses with unopened buds (tiny fiddlehead trusses). There will not be enough time left in the season for those fuits to ripen so the plant will be putting energy into alot of useless fruit mass. You will still have a few green fruit at the end of the season because the end flowers on the older trusses will continue to set fruit for a couple of weeks after the first flowers on the truss set fruit, but most of these fruits will be near full size and may ripen in storage.
You can also pinch off tiny new leaves at the top of the plant starting at about this time. Those left on the plant will grow to full size by the end of the season (and the plant itself will grow upward a foot or two) and the plant will not be putting resources into growing alot of immature leaves when it is loaded with fruit. This give you something to do while looking for tomato worms in August and September. A good strong thumbnail helps
Or you can do what most people do and not touch the plant and still have more than enough fruit for your family, friends, and total strangers.