It means that the host variable is a function parameter, not a local
variable.   Most of the time, there's not much difference.  However,
if you declare an array as a parameter, it is slightly different from
a local array.

In the specific case of 'struct sqlda **', there's no need to declare
it as a host variable.  The only place it would be used is in a
DESCRIBE statement, and you don't use the host variable notation there
(or, at any rate, you don't need to declare the host variable).