People complain that this enables cheating partners, but if someone is going to cheat, even the regular lock screen and other features and strategies could enable this.
Rather, I see this as useful for adding more security against phone snatching or other situations where someone might have your phone while unlocked, as much as you should proactively prevent that from happening.
Moreover, the feature can offer slightly more protection against abusive partners, rather than enabling cheating partners. What about that?
In any case, your phone is your phone, and your data is your data. You ought to be able to defend your privacy. In a relationship, talking is the solution, not snooping.