As mentioned above, the high end groups normally offer one or two of the latest features, and offer the lowest weight. Mid range groups are a few grams heavier, but usually perform as well or better, and may be more durable in the real world where bikes fall over, get bumped, etc. entry level stuff is often stamped steel instead of forged aluminum and bearings are another place they cut corners. I normally buy last years midrange "pulls" for about 25% of the price for this years equivalent. I leave the high end matching gruppos to rich folks who care about such things.