The attack itself provides no benefit to Iran, of course. No Iranian making strategic decisions would authorize the simple bombing. But another aspect of the attack, specifically Israel's response to it, is useful to other countries that are trying to weaken Israel in a different way. A lot of people follow the news and there is one very clear set of possibilities in the minds of most Israelis, another very different set of possibilities in the minds of most others.
Report: Russia, U.S. agree on full cease-fire in Syria for April 30 (DPA)
from the article: Iran denies involvement in Burgas bus bombing that killed five Israelis