A watch-only address means an address your wallet is tracking the balance of, and not more than that. To own an address, which means to be able to spend from it, one is required to know its private key. All addresses generated by a wallet software have their private keys stored by and known to the wallet.
A common scam using watch-only addresses is as below:
- A user is told "invest today, earn 100 times soon"
- The victim pays the malicious actor.
- Later the malicious actor says "We have your profits, now you need to import them to your wallet"
- The victim is instructed to import the address as "watch-only" to their wallet and not the private key required to spend the coins.
- It takes time for the victim to notice that they can't spend their balance. However, the malicious actor has already vanished.
Remember that Bitcoin is a cryptocurrency, which means it's possible to make transactions!!! If the malicious actor was honest, he'd ask for the user's address so that they could make a transaction and send their earnings, but importing to wallet should always be considered fishy.