Bug control, they eat ticks, and anything else that they can catch.
No ticks on 3 dogs in last 2 years (except when they decide to go through the woods and visit the neighbours) then they come home with ticks, so I know that there are ticks out there, just not in my yard.
I have eaten thier eggs, I sent a lot of eggs to BYCers that wanted guineas, and hatched quite a few out myself and sold them.
Havent eaten any YET, but that may come to an end soon, Some that I sold did become dinner, which is what that person got them from, and they want to raise more next year, so I guess I will hatch more when they start laying again.
The security alarm is just a bonus, and they alert the chickens/anyone within ear shot anytime anything is out of the ordanary stray dog, hawk,or the fact that I have on a hat etc....... gotta take the good with the bad.