Why should you eat mashed potatoes? I wish every question were as easy to answer as this one: you should eat them because VIRTUALLY EVERY COMMON VEGETABLE TASTES GREAT WITH THEM. If you're not getting enough vegetables then here's your solution.
I know, I know...you're worried about the starch. Well, the USDA gives them a clean bill of health and so do I. Listen, I had mashed potatoes almost every day for the whole time I was growing up and I was skinny as a rail. I always ate a decent amount of vegetables at dinner and I didn't even like vegetables. I only ate them because they seemed to go well with the potatoes.
And it wasn't just me. Lots of my friends ate mashed potatoes and none of us ever got fat. The girls pictured above probably ate mashed potatoes...everybody did when I was a kid and there were much fewer obese people then than now.
Later we became New Agers and turned against mashed potatoes in favor of rice, because it was more exotic. Big mistake! Vegetables can taste great with rice if the meal's an Asian dish cooked the Asian way, but if you cook a standard Western dinner and simply substitute rice for mashed potatoes, the vegetables suck, and you end up ignoring them. Some American rice eaters give up vegetables entirely.
I told this to a friend who was horrified that I'd even think of eating a potato. He was an ex-hippie who regarded potatoes as a CIA plot to make us lethargic so The Man could manipulate us easier. It's hard to know what to say to someone like that.
He regailed me with stories of vegetables he'd eaten in restaurants that were to die for, and which didn't require a bit of potato. Weeeeell, that's true...I'll concede that if you can afford to have a chef with a well-stocked kitchen cook all your vegetables, then you don't need potatoes. He can saute the vegetables in stock, give them a hint of mango, a little chervil ( a French spice not sold in most American supermarkets), three kinds of oil, expensive brands of balsamic vinegar, and top them with a little cognac....yeah, if you can afford to eat that way every day then you don't need potatoes.
So why not baked potatoes instead of mashed potatoes? Well, they taste great, but they don't blend with vegetables as well as MP. Also, they require chives and sour cream and those are pricey if the only time you ever use them is in small amounts on potatoes. They'll rot in the refrigerator (above).
So how do you cook mashed potatoes? My parents just boiled russets whole (not chopped up) til they were soft, put them in a bowl, peeled and chopped them, added whole milk, (nowadays most people prefer Half and Half) and a little melted butter then mashed them with a masher til the lumps were out. They were always eaten hot, immediately after mashing, with a side of cranberries, and with meat and vegetables. Yum!
I looked up mashed potatoes in the American Test Kitchen Cookbook and their concern was fluffiness. To get the lumps out they recommended buying a mill or a ricer (like a giant garlic press) to squeeze the potatoes into spaghetti which you stir into fluff. Right away I saw a mill on sale for ten bucks, and I bought it.
Okay, end of rant!
BTW: squash is the exception. It doesn't work with mashed potatoes.