They are very useful trees, with high-protein, edible pods that can be made into flour for human consumption. The young leaves are also edible.
Their flowers are fragrant in the spring, attracting many pollinators.
They are leguminous, nitrogen-fixing, farmer's trees. Their dappled shade helps other plants survive in the blistering heat of the summer.
When given adequate water, they grow straighter, and reputedly have fewer (or no) thorns.
Mesquite wood is beautiful, and has an extremely low dimensional change coefficient, making it a great choice for flooring in kitchens and bathrooms because of its excellent dimensional stability.