Not to be a smart%$^ but the idea behind the traditional DA/SA pistol is that the first long, heavy DA shot is supposed to act as a sort of safety. In other words the longer, heavier DA pull makes sure your intent is to be pulling the trigger. The idea rather right or not is that it is safer in theory than the earlier sngle action autopistols. They usually were some form of cocked and locked carry.
In other words a round in the chamber, safety on, and a light, short, trigger pull. 1911, and Browning Hi Powers for example. Many considered this form of carry inherently unsafe. The DA/SA also allows for a gun that is instantly ready for action similar to a revolver. Pull, point, shoot. Simple. DAO guns like the Sig DAK are supposed to be similar to revolvers.
The same long trigger pull for each shot. Some consider this to be the ideal type of weapon. Again requiring a long, to varying degrees with design somewhat heavy, consistent trigger pull. An auto that shoots like a revolver but has the advantages of an auto. Some combine both a DAO trigger pull with a safety such as the Para LDA's. A light DAO trigger with a grip and thumb safety. Each has it's own pluses and minuses. It all comes down to personal taste or mandate by department. Contrary to many folks feeings though as long as the gun fits your hand and has a decent trigger you can learn to shoot any of the guns well. Some just take more work than others.
