Burn vaults are a special kind of vault. They are used to manage the burn rate of fees, and have their own distinct benefits.
Say we have $10,000 in fees to burn. Most other yield farms would just take a portion ($1,000 for example), to buy back their own token and send it to a burn address.
This ends up with $9,000 leftover in fees and a bump in the token price temporarily.
Eventually, there won't be any more fees to burn. The price of the token will gradually trickle down to zero, as there is now no price incentive to farm.
Instead of the above, our methodology is to take the burning fees and stake them in a vault, for example 1ETH-1UST. We then burn the earnings from the vault.
Going back to our $10,000 example above:
That $10,000 is staked in a vault, generating a humble but consistent $30 per day. The key here is consistency: it will continuously generate $30 per day.