While many services want users to rely solely on their phones for 2FA, it's not feasible. Phones get hacked, lost, and broken, leaving you with no access to your Google Authenticator codes. Even if you're just being texted codes to enter, you're still stuck if you don't have access to your phone for any reason. By using your desktop, you don't have to rely on your smartphone to access any accounts that use 2FA via Google Authenticator. Of course, this only works as an alternative if you're just logging in to your accounts when you're at your computer.