This wasn't done to cater to families with multiple switches as I keep seeing people saying (though it is a benefit). It was done so people would be able to buy Limited Edition consoles, like the 3DS had, and switch between their own devices
Remember: Save transfers are a ONE-WAY street. Meaning you can transfer it from one console to another, but once you do, you cannot use the same user on the source console.
BE WARNED, FIRMWARE 4.0.0 STOPS THIRD PARTY CONTROLLERS WORKING. My USA 8bitdo snes30 no longer works. There is footage of the UK version working, but, it's laggy. I have both and neither work anymore.