Do they use them for anything? Are they perhaps just evolutionary leftovers? Why are they shaped the way they are (furry spheres on sticks)?
BTW, hello. This is my first post. 
hello! welcome to the SDMB!
This website…
http://nature-wildlife.com/girtxt.htm
has this to say about it…
If I recall my nature documentaries correctly, the males bash each other with their horns in mock battles in order to establish the alpha-giraffe.
That, plus the horns help to hold their hats on.