I prefer to do repairs on warm glass. While I do agree that "over" heating the glass closes cracks and causes an array of problems, I very strongly disagree that warming the glass to a suitable working temperature is the wrong thing to do. It's also no secret that when a viscous fluid like motor oil or windshield repair resin warms up it flows better so it's not too hard to figure out that breaks will fill faster if both the resin and the glass are warm rather than cold.
If any warming of the glass closes cracks we would have to conclude that windshield repairs could not be done in the summer time and glass should always be cooled to the lowest possible temperature before repairing. That is simply not the case! While my preference is to repair glass that is in the 80-100 degree range we all know that in the real world most of us will be doing repairs on glass that is considerably colder and hotter than that. Although not always possible, whenever I can I warm the windshield to as close to 80 degrees as I safely can before I start a repair. If I can't warm the entire windshield I will at least try to warm an area several inches around the damage and keep it warm throughout the repair process. I find it speeds up the repair process considerably and results in better repairs. My preference is to warm the windshield and resin first but as long as the the break is dry and the glass is approximately the same temperature as the glass when I start I find no fault in warming the glass after I start the repair process. I've done it thousands of times when time is a premium and had no problems as a result of doing so.
Now let's talk about moisture. Many of us have to deal with moisture on a daily basis. The best way I have found to remove the moisture is with heat but intense heat on very cold glass is obviously not a good idea so warming the glass before removing the moisture is a common sense move and one I practice religiously with excellent results. I agree with screenman that the glass should be cooled down after removing the moisture or even if the windshield is into the triple digit temperatures before repairing it, but to say that heating the glass is not good practice is simply incorrect.
Heat can be very beneficial when used correctly regardless of the type of equipment you are using, and can be very detrimental when used incorrectly regardless of the type of equipment you are using, so let's not mislead people into believing that just because they choose to use heat in certain circumstances they don't have the right type of equipment or are doing repairs incorrectly. Every windshield repair technician in the northern USA or Canada certainly knows better, as do thousands of technicians all around the world where drastic temperature changes are a common occurrence.
For me it always comes back to this. While we may not agree on equipment or methods, I've been doing this for 26 years and have have very few failed repairs or customer complaints. I can do repairs reasonably fast and I've seen enough of other peoples repairs to know mine are in the top percentile. Because of that I have always charged a premium for my services. If you can say the same you have my respect and I'll never try to convince you that you are doing something wrong. There is more than one way to skin a cat!