What are the advantages of using a rotary anode in X-ray tubes?

[tickle_monste]

I am planning to undertake the construction of an x-ray tube as a personal project with a friend of mine and I was wondering what are the advantages of a rotary anode? I'm having no trouble finding information on their construction, but have yet to run across the reasons for using one in the first place.

 

[daveg360]

http://en.wikipedia.org/wiki/X-ray_tube#Rotating_anode_tube

I'm a little concerned that if you have to ask that - you probably don't know enough not hurt yourself or others, if you go ahead with your project that is...