Address Reuse

Every time you reuse an address, you give the world another piece of your transaction graph. Block explorers aggregate balances by address, chain analysis firms correlate timing, and one leak (a doxxed donation page, a published payment request) ties every past and future transaction at that address to your identity.

Best practice is one address per incoming payment. BIP-32 hierarchical deterministic wallets are designed for this — they let you generate effectively unlimited addresses from one seed, so producing a fresh address for every invoice costs you nothing.

Custodial services and merchants who treat addresses as account numbers leak especially badly. If a service generates one address per user and never rotates it, every deposit and the user's full balance becomes public the moment that address is identified.