You create such wallet to follow up your wallet transaction, balance without needs to copy and paste your addresses to block explorers and check those details. Because if you use block explorers without Tor connection, you leak your information.
If you are using watch only wallet without tor, you are also leaking your information to the central server. Information like IP address and your wallet address.
Watch only wallet on tor is good to be anonymous, but if you check the information on explorer with tor, it is also good. Watch only wallet gives convenience to track your wallet, but offers more than that. Watch only wallet can be used to sign unsigned transaction and also giddy for broadcasting signed transaction in addition to its function.