If you do not have this you are at risk where if your property is damaged through natural disasters such as hail and tornado's, household issues like electrical fires, or vandalism in many if not most policies as well as liability issues.A umbrella policy is built to supplement your landlord policy. 

We are supplementing the occasional loss with gains from our other profitable Airbnbs.Not ideal!

Our financial goals are to supplement my and my 2 siblings’ incomes in the short term, and contribute to our retirement income in the long term.

No service is perfect.But when I ran the credit/background checks myself I could ‘read between the lines’ to get a pretty good picture of an applicant.Can’t do that with Cozy.Because of these limitations I'm considering using a different service, or supplementing with my own application.

Is it to supplement monthly income (cash flow), is it wealth accumulation, or a little of both?

We BRRRR 8-10 per year and the flips supplement and money left in the BRRRRs.We fund with a combination of Hard Money and Private Money. 

There are many good books out there on the subject, but asking investors directly helps to supplement that knowledge.Having invested out-of-state since 2004 myself, I have to agree with you that most of California doesn't make a lot of sense from an investment perspective.

Sure- i own one rental house free and clear, cost $80,000. i am 10 years away from retirement and will need to supplement my income with another $3,000 a month . i have $60, 000 cash to invest now.

I'd say capital is the main driver as to how many people buy, and second to that is really their goals--are they shooting for financial freedom, or are they just wanting some additional supplemental income?

Supplementing with flips, new construction or some other form of REI, keeps the interest there and actually pays the bills without having to use your cash flow to live and hence, killing the golden goose.