A Patronus is conjured as a protector: Patronuses shield their conjurors from Dementors, and can even drive them away. They are also used amongst the Order of the Phoenix to send messages. According to Fantastic Beasts and Where to Find Them, the Charm is the only known defensive spell against Lethifolds.
You might, for example, be interested to know that the word “prestigious” is derived from the Latin praestigiae, which means “conjuror’s tricks.” Isn’t that interesting? This word that we use to mean honorable and esteemed has its beginnings in a word that has everything to do with illusion, deception, and trickery.
By Cheryl Strayed from We are all Savages Inside in Tiny Beautiful Things