Purees Vs. Their Original Counterparts

Outside of somewhat increased oxidation risk, it shouldn't matter much.

And in a modern diet, it's fairly easy to achieve proper nutrition. I wouldn't worry much about nutrient loss in the general case in first world countries.

From the culinary point of view purees offer a textural variation and/or the chance to combine flavors and ingredients in different ways. They're considered "work" by most customers so is something they wouldn't do themselves making it more attractive from a marketing perspective.

 

This was in the local paper before Thanksgiving quoting Harold McGee:

— Mashed potatoes

So long as you treat them gently, it doesn't matter what kind of potato you use. "If you just mash them barely, what you end up with are intact little cells and clumps of cells that are surrounded by a wonderful mixture of butter and milk and whatever else you've added," McGee says. "If you break the cells open, that's when you release the starch inside the cells...That's when you get that gloppy, sticky result."

Purees, are usually done with power tools that will break up the cell structure with different results than mashing by hand that doesn't break up cell structure much if at all. Purees should be perfectly smooth, a mash should have a little texture left imho.