It's a practical feature in general, to allow anyone to poke through your phone without installing/posting/reconfiguring anything, occasionally nice to have. Then again, it would also slightly increase the social normalcy of being able to ask to snoop through other people's phones.

So they can use the banking app to transfer money away from your account because that's not stored locally on your phone? Or to look at your private photos?

Surely even banks/countries that do not have a stronger auth method require at least a password for login?