Heres some real world experience, 2 years ago I set up my 75 gallon. Once cycled I added 2 blue sapphire damsels as my LFS told me they were very hearty and I wouldnt have any problem acclimating them and keeping them alive. This was all fine and dandy until it came time to add more live stock. Added a lawnmower blenny and with in 24 hours the damsels had him so beat up I couldnt save him, they killed 2 clowns as well over the period of 2 months, clowns that were hosting a nem none the less, how they managed this is beyond me.
Once I finally decided to remove them I had to tear my entire tank apart, every piece of rock and coral had to come out just to net the little B*******, it took an entire day of tear down and re set up just to remove 2 little fish. To this day I have never experienced anything like it with any other fish and I for one will flush a damsel before it goes in my tank.