Well, I wish to learn Katon because one of my bios is an uchiha. The other reason is that fire seems quite useful in our RP. You can use it for many different ways. My other bio is a Nara, I could use the flames as a source of light to make my shadows stronger. Fire can also be used as a distraction, for example I could use a lightning style jutsu, then use a great fireball technique to cover it. Another way it could be used as an example, is if I use a fireball jutsu, then I could run straight behind it using it as cover while simultaneously using a chidori or rasengan. My opponent would guard against the fireball, but might be surprised to find me behind it and a rasengan in his face xd.