Why? Because some statements like VACUUM cannot be used together with any other statements with single -c option. The current solution is using echo and pipe op, but it is a complication in some complex scripts - higher complication when you run psql via multiple sudo statement.
Example:
psql -c "select pg_stat_reset()" -c "vacuum full analyze" dbname
or on all db
psql -At -c "select datname from pg_databases" postgres | \
xargs -n 1 -P 3 psql -c "..." -c "..."
Ideas, notes, comments?
IMO, rather having multiple -c args, it would be good to have another flag like "-C" which do accept and execute multiple SQL statements in sequential.