Difference for Binary format vs Text format for client-server communication

Hi:

Every pg_type has typinput/typoutput and typreceive/typsend
they are used for text format and binary format accordingly. What is
the difference between them in practice? For example, for a PG user,
shall they choose binary format or text format? Actually I don't even
know how to set this in JDBC. Which one is more common in real
life and why?

The reason I ask this is because I have a task to make numeric output
similar to oracle.

Oracle:

SQL> select 2 / 1.0 from dual;

2/1.0
----------
2

PG:

postgres=# select 2 / 1.0;
?column?
--------------------
2.0000000000000000
(1 row)

If the user uses text format, I can just hack some numeric_out function,
but if they
use binary format, looks I have to change the driver they used for it. Am
I
understand it correctly?

--
Best Regards
Andy Fan