It's a convenience. If you hold National Security secrets on your telephone, don't use faceid or touchid. Use a complex password only. Also, don't put servers in mom 'n pop stores either. That's not a good idea.
Seriously, I laugh when people throw out dramatic scenarios about the legitimacy of this. IF A COP POINTS IT AT ME AN RUNS AWAYY, WHAT DO YOU DO THEN HUH? GOTCHYA!!1
I mean, use a complex password if you are planning an attack or something. Otherwise if you want your cat/dick pics to stay safe, you are good with touch/face id.
Why do you take pics of your cat's dick?