I was wondering about this question for a while but never bother asking.. Maybe this is the right time and thread to ask 
what's the benefit of putting our btc on vault? does the amount slightly increases by time? Or... its just safer that way? and what's the difference with the basic "normal" wallet?
what's the benefit of putting our btc on vault? does the amount slightly increases by time? Or... its just safer that way? and what's the difference with the basic "normal" wallet?
If I'm not mistaken, Xapo vault is a way to keep your bitcoins on a cold storage, which is more secure than normal wallet because they are stored offline.
If you use a vault, you have to pay an annual fee that works as an insurance for keeping your bitcoins safe.
I havent used any vaults yet but I was just looking at the differences between Xapo & Coinbase which also has a vault option
How much does the Vault service cost?
It costs nothing! The Xapo Vault and Wallet are completely free-of-charge.
More info on the Xapo Vault
https://support.xapo.com/xapo-vault