Your PGP Key carries with it a set of "supported" algorithms -- ciphers, hashes, and compression techniques. These are useful so that if someone wants to send you information, they can look at your key, and pick only an algorithm that you advertise that you support. Similarly, when you encrypt data to someone else, PGP software will look at the recipient key to determine what algorithms your recipient supports and preferrs to use.
In general, people will be communicating with you using AES and SHA-2, and the only time one of the other algorithms will be used is if you are communicating with someone who has a very very old version of PGP software. If you feel so inclined, you could uncheck CAST, TripleDES, and IDEA. I would leave at least one non-AES cipher (such as Twofish), and I would turn off MD5, RIPEMD-160, and SHA-1 (if those are on).
Regards,