One of their greatest contributions was bearing the brunt of Iraq (supported by the West) aggression. Chemical weapons (supplied by the West) were used against Iran during the conflict, for which the UN did nothing. This was the basis for the next 2 wars fought primarily by the US. So yes, if you think containing Saddam was important then I guess they had an enormous impact. BTW It was the US that forced the Iranians to negotiate peace with Saddam, otherwise they would have finished the job themselves.
ISIS kills 22 in Yemen's Sanaa, Aden; targets both gov't and Houthi rebels (Reuters)
from the article: Medvedev: Israeli strike on Iran could spark global catastrophe