When a potato cooks, the starches contained in each cell are released as the cell walls break down. These starches absorb the potato’s internal moisture and swell and soften. These two processes are what transform a raw, hard potato into a cooked, softer potato fit for mashing.
If you cut your potatoes up before boiling them, the starches absorb the internal potato moisture as well as the water in which they’re being boiled. If they boil for too long, they absorb too much water and your mashed potatoes will become gummy. The difference between perfectly cooked potato pieces and soggy pieces can sometimes be as little as a minute or two.
An easy workaround is to boil potatoes whole. They’ll take a bit longer to cook but you can leave them in the hot water after boiling without undesirable effects, keeping them warm until it’s time to mash them. I start my potatoes boiling as soon as I begin cooking and mash them immediately before dinner.
If they need more moisture, you can add a bit of hot potato boiling water or another liquid. This way, you have more control of their moisture content.
Your explanation of why you make sous vide mashed potatoes because you can’t handle a 10 minute cooking time is hilarious, thanks.
Imagine being the kind of person that, presumably as an adult, you think it’s cool to mock people on the Internet. I hope that made you feel better about yourself.
Edit: JFC, you’re the original comment guy, AKA the quintessential “well, ackshally” ex-Redditor. You’re just upset because I pointed out that you can’t read, then you proved it a second time.
I understand the original post, it was presented as a solution to a non-existent problem instead of just an alternate method.