Different behaviour of concate() and concate operator ||

Hi ALL,

I need little help to understand, text concatenation.

concat function and operator || have different behaviour, if any input is NULL.

test=# select  'abc' || NULL;
 ?column?
----------

(1 row)

test=# select concat('abc', NULL);
 concat
--------
 abc
(1 row)

It has simple reason, concat operator || use textcat() function which is STRICT.

my question is 

1. Do we required textcat to be STRICT, why?
2. textcat() is used for concat operator ||, can't it possible using concat() function?

Thanks in advance.

Regards,
Amul Sul