Is there a tactical reason to wear balaclavas?

Security and prevent facial recognitions.

Have you ever been in a desert? If you had, you would know.

Hide identity, camouflage, keeps dust and sand out, keeps the face and head warm (just because you're in a desert or arid environment does not mean it doesn't get cold), flame retardation.

Did you know that wearing a bandanna around one's face was actually common among cowboys throughout the American West and not just done by bandits, as popularized in Hollywood movies?

The reason for this is that facial protection is very important for most people whose livelihoods keep them outside and/or in hazardous environments. We take these things fro granted in our insulated, modern world.

Soldiers may encounter everything from harsh weather to exploding debris. Even in the heat, the protection given from the direct sunlight is often an acceptable trade off.

We got the Nomex ones in Iraq to a) provide a fire-retardent barrier for our face in the event of an IED strike a b) to keep the sand out of our faces. I have seen the Iraqi and Afghan soldiers wear them to hide their faces so the enemy would not know who they were and be able to target them and their families.