Have you ever waited on a parallelized statement? Parallel execution is said to be fast, efficient, system-exhausting. Far from that! There’s a 10.2.0.4 x86_64 system with 16 cores and over 600MB/s write-IO ability, one statement running, one CPU burning, one developer waiting. For days.
Finally, at the end of the week, the admin is involved. Because people know, that the time when admins are working most efficiently is weekends and nights.