Why double fry French fries after blanching instead of just blanching and frying?
The double fry process is to make a crisper potato chip. Tests have indicated that less oil is absorbed too, so this is a general health benefit

The blanch process is mainly for mass production reasons to stop potato chips from sticking together when packed. It removes all surface starch. Cold water rinsing is all that is needed for home, small scale production

Cooling and drying the chips between steps generally makes for a better chip

The quality, and suitability of the potatoes is still probably got more to do with it than the cooking process



Interesting experiments at http://www.macheesmo.com/2010/02/the-great-baked-fry-experiment/