Other people have talked about hash arguments to routines; I'll look at a more general aspect.
The key advantage in my mind is organizing or clustering data into categories. I am defined by my clothing sizes, degrees, vehicles, etc. My degrees are defined in terms of the courses I took, the grades I got, the assignments I completed. My studies in "History of the Modern World" doesn't care about my clothing sizes or whether I have a skateboard. Aggregating data into hashes instead of independent variables creates a context, it makes it easier to understand relationships.
As Occam said: Entia non sunt multiplicanda praeter necessitatem.
