Well... while there are plenty of risks... there could be some "good" to be earned from it...
You could charge either a flat use fee for the season or you could charge a per-mare stud fee.
You won't have to worry about paying for his board, vet, and whatever other expenses that are covered in your contract.
You would free up space in your barn for a while and you wouldn't have the hassle of managing a stallion for a while.
If the mares are excellent quality, you can produce more quality foals out of your stallion without having to buy more mares.
Perhaps the lessee will be more motivated to show your stallion's get (for promotion) with their own farm name on the resulting foals.
If the stallion is new and you haven't had a lot of chance to breed him, you can get an opportunity to see what mares he crosses best with when seeing the resulting foals.
Those are some PROS that I can think of...
Be sure you have them get insurance and that you have an iron clad contract...
good luck,
Andrea