Have you done a 3 day test, and if so, how did you find it? What lessons did you learn from it?
What did you miss the most?
What did your other half say about it?
I've done a few now. First couple of times you have something missing. Nothing critical as you could survive three days just sitting down and living off your carpet but it helps sort out the basics.
With buy in it isn't an issue. Without buy in it is usually a case of them going away for the day to their pals. Not visited Auntie Cheryl for a while so see you...
I wish I had one day to myself to do something, let alone 3 days.
I've been a day or so without food a couple of times though, and found that OK as long as I had fluids.
3 day test of what?
Your bug in setup with grid down?
Your bug out set up?
A three day hike with BOB?
Your BOL set up and efficiency with grid down?
3 day testing of BOL is a good idea, but still slightly artificial as you know its coming and will subjectively have prepared for it even if you didn't mean to.
When grid goes down unexpectedly and without any warning, this tests plans more thoroughly, by showing up shortfalls.
As with everything, the greater the frequency of the unexpected power cuts the less unusual they become, and the easier they are to deal with.