to nostr:npub1yxp7j36cfqws7yj0hkfu2mx25308u4zua6ud22zglxp98ayhh96s8c399s s point

If I send to you (A->B)

and then you send on to C,

because I'm the sender I know the address that appears onchain for B

when you spend to C I could see that address appears as an input in the tx.

but I *cant* know if its a real spend or if it's just being used as a decoy by someone else.

but as STN says, knowing that IS valuable information, particularly if you have a lot of it (like a custodial exchange wallet). it would be better if the sender didn't know the address of the receiver at all, as in paying an LN invoice.