The Large Specs are generally the large commodity funds that are generally trend followers. Knowing their positions is considered helpful to traders in identifying trending markets.
The Commercials are dealers in the cash markets and are considered the "smart money" by many traders. Knowing their position is helpful in finding markets where the trend might have gone too far and large positions by the commercials are considered as indicators of over priced or under value markets. Changes in the net commercial position can be an important trend indicator WHEN CONSIDERED RELATIVE TO THE HISTORY OF THE RANGE OF THE NET COMMERCIAL POSITION.
CFTC Commitments of Traders