hashing is basically a non reversible way to encode something. (encode not encrypt)
For example it allows an application to store passwords in a database without the owner of the database be able to know the passwords even if he can access the hash data table.
It also allows the application to validate you in a very fast way as you only need to put the password in the application so the app can do the computation of the hash and generate a result that then is subtracted or compared with the one that is in the database table.
If it is zero then all is good if it is different then you have not inserted the correct password.
No decryption key is required to be inserted somewhere to get access to the contents making it more safe and fast.
for Encryption you require a decryption key to be inserted or stored somewhere in the system, the computation required for encryption and decryption of the data is also higher using more resources and it has to happen each time the data is accessed or updated.
In the example of the password table above if the passwords are encrypted then anyone who has the key could decrypt and revert the original password and that should not be acceptable.