Jim P, on some double action pistols, such as the CZ75, original Taurus 92, and several other earlier types, you had to manually lower the hammer to put it into double action mode after racking the slide. While on some you could simply carry cocked and locked (like the famous 1911) most people did not feel comfortable (some still don't) with the weapon set like that. So that is when you would lower the hammer manually.