There is symmetric encryption where encryption and decryption use the same key (e.g. AES, 3DES), and asymmetric encryption where encryption and decryption use distinct keys, and the encryption key can be made public without disclosing the decryption key (e.g. RSA).
We use both kinds of algorithms because neither can do all that the other can do. Symmetric encryption cannot offer the "public key" thing. Asymmetric encryption implies heavy performance issues, in particular data size expansion (and there is also a matter of CPU usage, though it is in fact secondary). If we restricted ourselves to just symmetric encryption, or just asymmetric encryption, then we would lose on functionalities. We really need both.
Hybrid encryption is the commonly used terminology to designate an assembly of a symmetric encryption algorithm and an asymmetric encryption algorithm (or key exchange algorithm).