It's natural to"better" it is. And additional pieces are often discounted when added to a set. "Why get the small set when you can get the large one for just a few bucks more?" the thinking goes.
There are a few problems with this logic. First and foremost, most hobbyist chefs do not need all of the knives included in a large set. Having four different paring knives might be useful if you're a professional cook and need to have the perfect tool for every task but, for the rest of us, it's overkill.
The other problem with buying a set loaded up with extra pieces is that those extra pieces are often just "filler". Adding 7 steak knives to a set is a popular way to bulk it up, as is adding a kitchen shears, sharpening steel and knife block.
You may want some of those items but, if you're trying to get the best bang for the buck, focus on getting the best "essential" blades. You can always add those extra pieces later. Those extra pieces are likely to be quite inexpensive when not purchased as part of a set.