Sneks eat a lot of rodents and various garden wreckers. Unless you live somewhere where they are poisonous and bitey, they are fine. Non-poisonous snakes far outnumber the poisonous ones.
Alon with bullsnakes, they're extremely useful for getting rid of said rodents—which CAN carry awful pathogens, like hanta virus!
Fortunately, snakes will generally leave you alone unless they're provoked or cornered. Unfortunately, if you have curios animals (cats, dogs) it can be a much more significant problem!