I don't know what would be useful to anyone on it that could harm you.
Even if you have a old Live profile still on there, there's no way to log in with it anymore and I don't think cc information associated with a XBL account was ever stored on the console itself anyways (Rather, it was part of your account's information stored by Microsoft on their servers).
And if you have some nice DLC on there, that's a plus when it comes to selling it since it will increase the value of the unit since it's not easily available now unless you mod the console.
So if you have things like the Project Gotham 2 booster packs, any XBLA games for the original Xbox (There were probably about 25 games releases for the original XBLA), and so on, I'd make sure to advertise the fact if you're selling it yourself on somewhere like Ebay and just aren't trading it in to some independent game store (GameStop doesn't accept Xbox 1 trade ins now, and they wouldn't of cared anyways since they always cleared the drives before reselling it).
If you have any concerns, delete any XBL profiles still present since there isn't going to be any sensitive personal information in your game saves. No need to clear the drive, the next owner down the line might be appreciative that there's some DLC, game updates, etc. on it if they have any of the same games you did.