Is it considered bad practice to have a wallet "cloned" on both a smartphone and a desktop PC?
It is merely a question of security. If your copy of the private key in wallet A (phone) is compromised, you can lose your coins. If your copy of the private key in wallet B (PC) is compromised, you can lose your coins. 

Assuming both copies are secure, you basically just have a backup of your private key.

As for whether or not having two copies like that is secure or "best practice", that depends a lot on how you handle your computers, and there are better experts out there that can answer that.

One thing you cannot do is double spend. If they use the same private key, one wallet is the same as the other, and trying to spend out of both will result in an unconfirmed transaction on one of them.