The DesertCraft mod is a simple tweak to add more to desert biomes. Vanilla Minecraft seems to be a bit lacking when it comes to deserts and this mod aims to fill them up a bit. Now you have more cactus varieties, flowers and dry grasses.
But the mod also adds a bit more use from cactus and sand. You can now make cactus armor and tools. They have about the same durability as wood or gold but they make for an extra utility to make tools and armor early on in the game, especially in more hardcore environments and if you happen to spawn in the desert.