If the hash function does its job at mixing input, this is no different than applying just the final hash. (With the technical caveat that doing at least two s

If the hash function does its job at mixing input, this is no different than applying just the final hash. (With the technical caveat that doing at least two serial hashes does improve the properties of the hash function by defending against length extension attacks. That's why things like HMAC do multiple chained hashes. But it does zilch for collision or preimage resistance.