Flash Loans are uncollateralized loans that must be repaid (with interest) in the same transaction that they are borrowed. By consolidating multiple pools' tokens in the Vault, otherwise fragmented liquidity can be lent in a flash.
Asset Managers improve the capital efficiency of trading pools by reinvesting idle assets. Typical trading pools with deep liquidity benefit only from low slippage, but tokens not involved in trades do not contribute to the fees accrued by the pool. Asset Managers tap into that otherwise idle capital, using it on external protocols.