There comes a time when you need to put out a cigar, but I want to state upfront that there is no need to do anything but leave the cigar on the edge of the ashtray to put it out (no need to mash the burning foot of the cigar into the ashtray and create a stinking mess). The question is when should you put out a cigar? Some ill advisers will state that you should smoke it to the point that the cigar is too hot to be held. Others will tell you that you should put it out in the 2 third of the cigar before the burn line gets to the label. These are all wrong in my humble opinion and here's why.
Firstly, holding the coal to the point that its too hot to hold means that you have gone to far. As you draw on the cigar the toxins and carcinogens are also being pulled to the head of the cigar along with the smoke and trapped within the layers of the wrapper, binder, and filler. This is a good thing because it prevents the worst part of the smoking experience from entering the mouth and the blood stream (lets face it this is not the healthiest activity you can engage in). Furthermore, if you are frequent smoker this should become and even more important rule not to live by because the more you smoke the more you flirt with the daylight between enjoying a passion and sacrificing your health. In other words, the more often you smoke the more cautious you should be of smoking too far and allowing some pretty nasty toxins to the only body you have.
Secondly, putting a cigar out too soon is better than too far but its not practical and may encourage you to smoke more than one cigar at a time. In addition, it will cost you to put out a cigar that soon because you have not fully consumed it thereby wasting a perfectly good smoke and denying yourself of the pleasures of the last third.
My advice is as simple as it gets. Put the cigar out when it gets between 1.5 and 2 inches long. This is a safe way to prevent the bad stuff from entering the body, having to deal with a charred taste, and wasting a good cigar too early.