Dad’s short answer: One if your home is small and mostly one surface type. Two for most families — a main floor vacuum plus a handheld. Three only if you have a lot of carpet and want cordless convenience on top of corded power.

The combinations that make sense

One machine: small home, mostly one floor type, no pets. A good cordless stick on hard floors, or a corded upright on carpet, and you're done.

Two machines, where most families land: a main floor vacuum plus a handheld. The handheld covers the car, the stairs and the furniture — the jobs your floor vacuum is genuinely bad at — and it's the least expensive of the three types, so it's an easy add.

Three: a corded upright for the deep clean on carpet, a cordless stick for daily, and a handheld for everything else. That's my setup, and I won't pretend it's necessary for everyone.

Adding a robot vacuum changes the math again — it takes over the daily maintenance, which reduces how much you need a cordless. Plenty of people run a robot plus a corded upright and skip cordless entirely.

Where people waste money

Buying a second machine that does the same job as the first. Two mid-range cordless sticks isn't a strategy; one good one and a handheld is.

Buying a premium machine for a job you do twice a year. If the stairs are the problem, that's a handheld, not a bigger upright.

And buying for the house you wish you had. Buy for your actual floors and your actual pets.

Dad’s Take: Two machines covers most families: something for the floors, and a handheld for everything the floor vacuum can't reach.