Lights are the worst thing you can use if you are the lone defender. As soon as you turn on the light the bad guys know exactly where you are. They are great for a swat team with a dozen guys.
This comment is much more effective in showing your lack of knowledge concerning how to properly use a light and other HD tactics than it is in showing that lights are a bad idea.
You should open a training center since guys like Clint Smith and Pat Rogers are giving out such bad advice and training.
Because warnings, of all kinds, save lives. Yours as well as the other guy.
The type of threats that require responding with a firearm are not monolithic. While it is true in certain instances a challenge (aka warning) be it verbal (e.g. stop, stop or I'll shoot, get out of my house, I have a gun, Do not come any closer, etc, etc) or the racking of slide, may dissuade someone and be enough to end the threat it certainly is not in all cases. In many jurisdictions one is under no legal duty to issue a challenge prior to using deadly force. Where I live doing so does not play anything approaching a dispositive role in the permisability of using deadly force. Nor would it be in a civil case.
Use of deadly force can be seen as a triangle with three important points. The above mentioned legal factors. Second is tactical considerations. In some circumstances issuing challenges may make sense. In other situations doing so might be a horrible idea. what is a tactically sound or even reasonable action is highly fact specific and blanket statements often fail on account of that. Being silent or acting immediadetly might save lives in a circumstance where a warning gets you hurt or killed. Take the example of the CCW holder who left a shop in the mall and encountered an active shooter on a rampage. He sees the kid shoot someone and draws his weapon but instead of firing yells to the kid to put his gun down. The kid whipped around and shot him. A warning was not tactically sound or appropriate in that case. It takes little imagination to come up with a HD scenario where immediate action would be better than any form of challenge or warning.
The last point on our triangle is the morality. Much of this is so subjective I will not bother to address it at length. I will simply say I can imagine scenarios in which morally I would view a challenge as appropriate and others where I would not.
In sum, a warning/challenge could theoretically save lives, it could also get you killed. Its appropriateness might have to balance legal, tactical, and moral concerns. Depending on the exact situation that calculation might come out differently.