I don't really see the issue. If you don't want the face recognition feature, then you'll turn it off once, and that's that. Maybe if you're unsure, you might turn it off, and then back on, and then back off again. But what's the use case where you'd want to do this more than 3x per year?
Presumably, it's somewhat expensive to run face recognition on all of your photos. When you turn it off, they have to throw away the index (they'd better be doing this for privacy reasons), and then rebuild it from scratch when you turn the feature on again.
Presumably, it's somewhat expensive to run face recognition on all of your photos. When you turn it off, they have to throw away the index (they'd better be doing this for privacy reasons), and then rebuild it from scratch when you turn the feature on again.