Proof of reserve is good for first movers as a flex of power. 

In general it's a liability. Consider a war, if your enemy knew how much your defence cost it could estimate the cost to overwhelm you. 

Even if you successfully fend off one attacker, other enemies could calculate your vulnerability  

 transparency is double edge sword ! just like nobody know if america really have real gold in fort knox or certain stats M0 M1 which fed stopped publishing 

 Yeah, it's good for other people.