The same benefit you receive by being an avampirist and an aleprechaunist - freedom from a false, oppressive belief. There is no advantage to dedicating time and other resources to a false belief. As an avampirist, you sleep more soundly at night and don't waste your garlic on nonexistent monsters.
As an aleprechaunist, you are relieved of the futile search for the pot of gold at the ever elusive end of the rainbow. As a secular humanist, I am spared much. Sleeping in on Sundays and using what would have been thrown into the collection plate to attend to my family's needs rather than those of some priest or preacher is a great reward.
Also, freedom from the terror of hell theology That's good. How about the comfort of knowing that when later today, some doe-eyed child dies from leukemia, that it was just rotten luck, and not the plan of some malevolent or indifferent deity.
I have lived both within and without religion. The latter is preferable. That's the advantage, which was lost to the first theists.