then Sammael has been one of the most competent FS (aside from his misjudgment of Rand's aggression and his subsequent death). Of course, most of this is without intention.

1. He unleashed the Aiel in the West, occupying Perrin as well as the most fair-minded Seanchan we've seen (Tylee).
2. He killed Herid Fel, who is the only person thus far to come close to helping Rand with the LB.
3. He sent the gholam to find ter'angreal, and it found the Ebou Dar cache and starting hunting Mat (since Sammael died around that time and couldn't change the order).
4. Even after Rand defeated him in Illian, Sammael left enough strife and corruption there to push Rand towards becoming Dark Rand in his campaign against the Seanchan. I'm pretty sure that one of the two female nobles following him was the DF we saw in the tGH DF social. TPoD was a turning point from Rand, probably where he first started to use anger and bullying as his modus operandi. All thanks to the disorder left by Sammael (specifically, the corrupt, incompetent nobles).
5. Choosing SL as a battleground forced Moridin's hand, and lead to (a) the Balefire sickness which makes Rand virtually unable to channel and (b) he saw Liah there, which was for him like doubling the length of his list of the dead.

Not bad at all when you consider that none of the above were really intentional. Even the Shaido were never intended to do more than create a little chaos far from Sammael's lair.