any benefit to preparing a sql function?

Is there any benefit to preparing a call to a pre-defined sql function
or is the sql function already optimized?

create temp table foo(col1 integer);
insert into foo(col1) values(1);
insert into foo(col1) values(2);
insert into foo(col1) values(3);
insert into foo(col1) values(4);
create or replace function testfunc(integer) returns foo as 'select *
from foo where col1 = $1;' language sql;
prepare myplan(integer) as select * from testfunc($1);
execute myplan(2);

They look exactly the same:

testdb=# explain execute myplan(2);
                           QUERY PLAN
-----------------------------------------------------------------
 Function Scan on testfunc  (cost=0.00..12.50 rows=1000 width=4)
(1 row)
testdb=# explain select * from testfunc(2);
                           QUERY PLAN
-----------------------------------------------------------------
 Function Scan on testfunc  (cost=0.00..12.50 rows=1000 width=4)