From my perspective now that we eat whole food plant based, no oil, no refined sugar, little salt.....a lot like a vegan without the junk food, that many people talk about this challenge. The increased chopping of food. Most of the food needs to be sliced or chopped or ripped apart and they don't like doing that. They don't like doing it daily, they don't like doing it for an hour for batch cooking on the week-ends, they don't like chopping. I don't mind the chopping.
I mind
how dare the greens cook down so far!
I get 4 bunches of greens, lately collards and mustard, and that only cooks down to 5 cups of greens and I eat greens daily. I've canned them but my frustration with that is having a full cooler of greens from the garden, washing and soaking out the slugs/worms/bugs, then a final wash, then steaming, and I don't even get a full canner load of 7 quarts.
On the bright side, cooking takes so much less time, oil doesn't show up on my floor, stove, oven, dishes, cabinets which makes cleaning fast and easy. Whole grains and legumes take the longest to cook, so I do batches, and that could all be even less time in an instapot if I decided to go that way.
My friend with 10 mouths to feed went to eating this wfpb'ed way a couple years ago and was thrilled how much less time she and her family needed to spend preparing foods. With 10 mouths to feed 3 times a day it was a pronounced reduction in time needed to cook.