I believe she means that if she wanted to take a picture of a devilishly handsome Elezen gentleman who never smiles (for good reason), she could enter Group Pose mode and smile to force him to smile as well.

The appeal is self-explanatory but at the same time some (primarily Japanese) fans will probably feel uncomfortable with the idea that someone else can effectively force them to do things they didn't actually do, in secret. Perhaps I'm wrong about that, but I can easily imagine some people finding it irritating.