This lets you wield weapons in combat. Most people don’t need this during daily play, which isn’t to say it’s useless.
If your spawn form drops while fighting, this will let you arm yourself again. If your party leader rushes into combat before you’re ready, you can at least wield your sword if you have this skill. There are even cases where you might want to open combat without your preferred weapons wielded. Switch weapon is the thing to have in these instances.
The ingame help reads:
Skill duration: random. Type of skill : neutral skill. Affecting stats: Dex. It uses no endurance points. Some of the more powerful fighters in the land, do a little showboating. During a fight, they toss their blade from one hand, to the other. Some are able to do this with a blade in each hand, tossing them both in the air and catching them in different hands, all while not missing a beat. While most of us might not feel comfortable tossing our weapons in the air during a fight, being able to change weapons can come in very handy. Some weapons are better against some foes, and who knows, maybe a little showboating won't hurt a little?