Oracle / PLSQL: CAST Function

What is the user of CAST function ?

The Oracle/PLSQL CAST function converts one datatype to another.

select CAST( '25-Mar-2019' AS varchar2(30) )
from dual;

convert ROWID to char 
select * from t1 where cast (rowid as char(5)) = '01234'; 

convert string to timestamp 
select cast('25-Mar-2019' as timestamp with local time zone)
    from dual; 

select product_id,
    cast(ad_sourcetext as varchar2(30))
    from products;