security that you don't have to worry leaving any amount to your account..that you are sure that anytime you want to go back, your funds are intact.
also responsiveness of the support staff is a big plus for the site
Let me remind you that being able to store funds in a vault system is a good thing but this should not be considered to be an alternative to wallets. You should always store coins in your personal wallet.
Besides if you ever see your funds missing then you are being scammed, specially if its some casino you never heard of before, but obviously you will have done some research before betting there.
Having a responsive support team is one of the backbones of the brand name of any casino. I hope every new casino names recruits a good team for this purpose.