Powder coatings aren't applied in the typical paint method. That is, the paint isn't in liquid form, and it isn't thinned or reduced with another catalyst agent that will evaporate.
Powder coating generally involves an electrostatic system of applying powder to the item, which is then heated to 400°F to allow the coat of powder (hence the name) to fuse together.
Due to the heat required to "cure" the material, this is already a "hard" paint. Additionally, you know that it will be literally FUSED to the piece. Also, the amount of time to get this finish is relatively quick as compared to the older spray system.
The biggest advantage over sprayed coatings is that since it has literally been melted onto your piece, there are usually no seams or gaps in the coverage. Additionally since there are no solvents within that need to evaporate, the porousness of the coating is literally nill. This makes for a very smooth and impervious finish.
It presumably is more tolerant of the effects of heat than paint. But it ain't a miracle. People who have powdercoated their headers have watched it burn and flake off in a matter of minutes.
Powdercoating can make a dramatic difference in the appearance of many parts. Powdercoated sway bars, springs, brackets, etc., really look nice for a long time.
You gotta prepare the surface just like if you are painting. Kill all the rust, sand, grind and smooth it out. It is a very forgiving coating -- but it will not mask all imperfections. When I powdercoated my heavily pitted, dented & corroded oil pan, it's looks improved 100% -- but it's far from perfect when you look close.