pg_dump: what is advantage with schema and data dumps?

Hi,

I've seen in previous posts that recommended practice for database backup is
to run the dump utility twice.   Once for schema only and a second time for
data only (I think).  Up to know, I've only ever dumped both, and have never
had a problem restoring into older/newer versions of postgres, nor with
restoring into other commercial versions of postgres.  This is a testament
of the robustness of pg_dump!  Of course, there are always a series of error
messages at the start of each restore when duplicate/unknown template DB
functions are recreated, but these have never prevented the core data from
being properly copied into the database.

Am I setting myself up for disaster with only a single dump as a backup?

Much thanks,
Peter