Although... if you have

CHAR(2)

And

VARCHAR2(2)

and the you know the value of the field will ALWAYS BE TWO. Then you'd be better of storing in a CHAR. VARCHAR2 use an extra byte to store the number of bytes used. In the example above... Char(2) would only use 2 bytes and Varchar2(2) would use 3.

Therefore valus that are always consistents, like Gender m/f, would be a good candidate for a CHAR(1) field.

Cheers,