How is it vulnerable (e.g., to a drop in rents)?

It's an option.  4 points are what an insurance underwriter would use for property insurance because they are the 4 most vulnerable points of insurable damage but a 4 point is 4 things - heating, plumbing, electrical, roof.  

Arlen has another idea on helping vulnerable populations overseas.. but I'll let him share ;)Ironically, I just arrived in Taipei from the Philippines!

The ones who are the most vulnerable are the small or medium sized landlords and they know that. 

Although It sounds like this scenario does make me a little vulnerable, since there will be access to several of my properties, it reduces the paperwork and still separates the business from my personal investments.

Given that the TN owes its existence to NAFTA, it is much more vulnerable to unilateral executive action than say, the H-1B. 

Stress causes physical problems such as depressed immune systems that can make one vulnerable to infections, flu, and even cancer.

It is also a larger house (with a large mortgage), so also more vulnerable to bad tenants who don't pay the rent. 

The vulnerable low income tenants can only see forever increasing rent with this out of balance ecosystem.

It also makes you vulnerable to "betting the farm" on the next big deal....The key to being happy with your investing (or any other) results is to define what success is for you and then work to achieve it.