[nemild]

> A number of transactions looked enormous but turned out to be some form of washing e.g address X sends $100MM worth of bitcoin to two addresses, with ~$1k going to address Y and the rest going right back to address X.

Bitcoin is based on the UTXO model, and requires the full amount of an input to be sent. For example, I might need to transact 20 bitcoin even if I only need to pay 1 bitcoin, with 19 bitcoin being transacted to a "change" address.

More by googling Bitcoin change addresses: e.g., https://support.blockchain.com/hc/en-us/articles/44170823927...