It's better for your own privacy and security to have a password with your bitcoin wallets. It takes half a minute to set one up and you can literally enter whatever you want. If you try to save time on something as insignificant as this, it will become a habit and you will decide to take shortcuts elsewhere. Better not do it.
If his Electrum version is 4.1.0 or above and he has another regular wallet(s) then I wouldn’t advise him to use a generic password.
The reason is because Electrum (mobile version) since version 4.1.0 no longer allow users to set different passwords for different wallets. So, if you update the password for one of your wallets (the watch-only in this case), all your other wallets will be encrypted with that new unified password.
That's right. Luckily, you can always go into your wallet details and change a simple password to a more complex one, and like you said, it will become valid for all other wallets from that point on.