My grandmother did this back in the days before Messr Robuchon and his wonderful cookbook. She insisted it was essential. And she was Irish and lived in Maine... so she knows about potatos!
The reason she told me was because it is too easy to forget to salt the water if you don't work in an organized and methodical way. I think she's right.
My wife does nto subscribe to this philosophy so I often have a burn on one of my fingers since I'll dip a finger in the boiling pot to check for salt in the water. It is better to get it in "too late" than not at all.
The only danger I know of from adding salt to boiling water is that it causes the water to "explode" when the salt is added. That never happens if salt is added to cold water.
Originally Posted by French Fries
Anyone knows what that reason is?