this video that @lost_in_time@hexbear.net posted goes over things, it's not known for sure, but aside from aesthetics, some potential practical applications are:

• aiding in binding the blade to an opponent's weapon, particularly for things like zweihanders which were used against pikes - so you'd try to hit the enemy's pike and move it out of the way, with the wavy blade helping your sword to dig into the pike's shaft and allowing you to control it

• preventing blade grabbing - while it seems pretty scary to grab even a normal blade, there are historical manuscripts which demonstrate techniques like that (definitely not something to be used as a first resort, but still applicable in specific situations - getting your hand sliced up is better than getting outright killed, after all), and a wavy blade makes getting a proper grip on a blade (where you don't get cut up) a lot harder

• possibly for creating worse wounds in certain contexts, like hunting