[tokenizerrr]

> You can as long as it stays the same over time. Either lookup salt by username (requires an extra call back and forth) or use a single salt for the whole site, or actually you could have the salt deterministically depend on the username. All of those defeat hash tables.

And here you just answered your initial point.

> If the salt changes, you'd need to compute the password using multiple salts, which might have crypto guarantee issues when sent to the server.

[ikeboy]

If you're using different salts for each password and sending them from the server each time (the first option above), then my point still applies: the client would need to send the same password hashed to different salts, which may weaken security guarantees. (I don't know if any hash algorithms could be exploited using this, though.)