Sorry for the late response time, been busy today.
1. The main reasoning behind using deadener is to get rid of the strutter-bornce noise found inside vehicles. This noise comes from a multitude of sources, including the engine, transmission, road and tire, exhaust, etc.. You get rid of these vibrations (which causes the noise) you create a much quieter and better listening environment.
2. Depends on the vehicle and goal. The vibration mats and liquids are used to control panel resonance/vibrations but won't actually stop or block air-borne sound/noise which can be caused by exhaust, road, and tire noise, as well as wind. For this type of noise, use of an actual barrier is needed, something like mass loaded vinyl.
3. Just like several other members have said, there is no need to go balls out and do 100% coverage. 25% is really all that is needed.
Doors are my first area to treat, followed by the floor, and roof. In a truck I would do the back wall right after doing the doors.
And thank you guys for the awesome input, makes my job just that much easier!
Damn you get paid to surf the forums all day? SWEEET.
...on the side did the Singapore distributor contact you guys for some alpha damp pro? Not sure if he can be trusted yet and I need the things now. Feel free to PM to prevent further thread jack