It can help someone blend in and avoid being recognized. Like in a spy movie, a disguise can help the spy complete the mission without getting caught.
One possible theme could be self - discovery. The girl in disguise might be on a journey to find out who she really is. Another theme could be deception, as she is in disguise, so there must be some element of hiding the truth.
One possible theme is the exploration of true identity. When love is in disguise, the characters often have to figure out who they really are and who the other person truly is.
The book,"Disguising Swordsman", meets your requirements! The protagonist was proficient in the art of disguise. He transformed into the Thousand-faced Swordsman and used the art of disguise to do the case. The plot is tight and exciting. I'm sure you'll like this book. I hope you like this fairy's recommendation. Muah ~😗
One possible plot twist could be that the king falls in love with a commoner while in disguise and has to figure out how to handle this relationship when his true identity is revealed.
It could be a way to drive the plot forward. For example, his disguise allows him to access places or information that he otherwise wouldn't be able to. This then leads to a series of events that form the core of the story. Say he disguises as a servant in a wealthy household. Through this, he overhears important conversations among the family members or discovers some dark secrets of the house, which then propels the story into different directions.
One possible theme could be family loyalty. The mom's disguise shows her dedication to her son and family despite the need for secrecy. Another theme might be identity, as both the boy and his mom may have to question who they really are in the context of their wealthy and somewhat secretive situation.
I'm not sure as I haven't read the specific 'the man in disguise novel'. It could be the protagonist who has some secret mission or is trying to hide his true identity for various reasons like escaping from enemies or uncovering a mystery.
One use could be for educational presentations. It can make the slides more interesting and relevant when you are teaching about storytelling or students' activities.
One possible plotline could be that Naruto discovers a set of enchanted knives that give him new powers. He then has to learn how to master using them while still keeping his ninja skills intact.
One use is for easy dressing. The zipper on the back makes it quicker and more convenient to put the coat on the dog compared to buttons or snaps. Another use is for adjusting the fit. If the dog gains or loses a bit of weight, you can easily zip it up or down a bit to make it more comfortable. Also, it can be used to attach accessories. For example, you could attach a small pouch to the zipper for carrying treats or a poop bag.