Cath play is something that can be extremely fun and stimulating, but has to be done the right way.
In a fetish/play sense, I learned to cath as a top from Rocket, who was the first one to do it to me.
He made a very good point about learning to cath someone:
If you want to learn to cath someone else, you should first learn to cath yourself -- learn to do the whole procedure to yourself at least once. Go over it in your head, ahead of time. Learn the process and feel the sensations that you are going to cause someone. Keep in mind that everyone feels urethral play a little bit different.
This isn't something you should learn on your own -- you should have someone teach you that knows how to do it, and has experience.
The Fun Parts (To name a few):
- Very Stimulating
- Intensely Controlling
- Aesthetically Interesting
- Good for Recycling Scenes
The Risks (These are the reasons to be careful, and do it under the most sterile conditions possible):
- Damage of the Urethral Tract from Rough Insertion
- Damage to the Bladder from Rough Insertion
- UTI infections
- Transmission of STDs
I have always been one to advocate both the risks and the benefits of any kind of play.