It’s All About Technique
Generally, a beard or mustache will make a face appear slimmer, longer, etc. For example, somebody with a round face can appear to have a sharp(er) jawline if the facial hair is trimmed with specific, harder angles.
On the other hand, if somebody wants to hide a pointy chin or a generally narrow face, this can also be done by for example sideburns that flare on the ends to make the face appear wider overall.
When it comes to facial hair, you can adjust it to the needs of your face. Even though it is known that generally, facial hair makes the face appear slimmer, there are tips and tricks to make a narrow face look wider.