It's super frustrating when you work with investors every day, and the common refrain is I want to buy a passive turnkey property, but it must cash flow.

IF the City does not limit to four total, there is a scenario where the City MAY allow up to 10 total units on single family zoned parcel

I don't see the value there....paying a plumber to come re-iterate common sense. 

It is not illegal as long as they aren't hidden and aren't in bedrooms or bathrooms...I have two in the common areas.

You may end up needing to go through the whole foreclosure process which can take a lot of time and cost a lot of money, and you may end up getting the property back in much worse condition than when you sold it, potentially with a squatter in it and months of lost rent, and in a worst case scenario you will be in a much worse position than if you had just sold it outright. 

What's the worst case scenario? 

Also makes it easy for each individual to maintain their own info in multi-owner scenarios.

And puffing ( again not saying he is puffing) is very common in RE.

Another case where common sense isn't so common.My $0.02 ...

The common feedback I hear typically revolves around your accounting preference.