I was reading about the life of Rabbi Zera, and it said he was originally a Rav. The Rabbis of Eretz Yisrael offered to confer on him the title of Rabbi and at first he refused, until they told of some special spirtual attributes he would gain and then he accepted.
So what was the difference in Talmudic times between a Rav and a Rabbi and what beneficial about the later?
Here is where I originally read about it in Wikipedia:
Ze'era was highly esteemed by Abbahu, the rector at Cæsarea, of whom he considered himself a pupil. He was ordained rabbi, a distinction usually denied to members of the Babylonian school, and though in the beginning he refused this honor (Yer. Bik. 65c), he later accepted it on learning of the atoning powers connected with the dignity (Sanh. 14a). Upon receiving Semicha, his title changed from Rav to Rabbi.