That could help to conduct a doublespend btw. A hacker accumulates a lot of PoW in legit small transactions forming huge amount of new tips, but doesn't broadcast them. Then he sends a legit transaction, waits for it to be confirmed, gets his purchase sent to him. Then he creates a doublespend (for example sends the same money back to himself) and floods the network with his precomputed legit transactions. So network hashpower now is spread over his tips and he needs much less hashpower to create enough transactions confirming his doublespend to overtake the first transaction.