Throughput.
As soon as you have >1 persons, you are going to find the bathroom to be a bottleneck at some point.
As soon as you have >1 persons, you are going to find the bathroom to be a bottleneck at some point.
I don't want to shower and brush my teeth just a meter away from the toilets.
https://q-cf.bstatic.com/images/hotel/max1024x768/214/214010...
Dual toilets have rescued us twice now from inevitable accidents.
No one wants to hold it while the other person is having a nice relaxing poop.
Toilets are a bit trickier, but if you're spending enough time on the toilet for it to be a bottleneck in your hosuehold, you may want to consider adding more fibre to your diet.
Need in the sense that, it improves the quality of life, and it's a worthy expense.
Additionally in the very large houses the bed/bath ration doesn't capture the setting of the bathrooms. There is a house not to far from me that has a connected indoor pool and that has 3 bathrooms for changing/shower.
(edited)
These aren't small houses.
I have a very wealthy relative who lives in the USA, and I visited when my younger brother was just 6 years old. It took him several complete tries of running round the house to count all the bathrooms (and not lose count).
There was one per bedroom, then one on the ground floor, one by the garage and one which was easy to get to from the beach.
The neighbour's house's guest room's bathroom was also the general bathroom; it had two doors with appropriate locks. This seemed like an efficient design.