I had a nasty rough idle that wouldn't go away after 2 years, over 70K miles, and several tuneups and 2 changes of plug wires. Finally I busted a ground strap when working on something else; when I replaced the strap with a new one the rough idle smoothed right out.
Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.
If you take a light that is supposed to run on 12vdc, and you operate it at 11vdc, you will generate more heat and reduce the life of that item.
Um... no. Not generally.
If you run a regular 12VDC tungsten filament light at 11V, you will generate less heat and increase the life of the bulb.
You're at least partially correct in specific cases. For example, certain motor configurations will draw more current -- and thus run hotter -- at lower voltages. Reducing the voltage too far on a halogen light can shorten its life by breaking the halogen cycle, inhibiting filament replenishment and causing occlusion of the bulb... but this is due to lower temperature, not higher.
To believe lower voltage universally equals hotter operation and shorter life is incorrect. Your suggestion to look up information on whatever particular item or system you're concerned about is a good one.