Sometimes, you're limited to a single tiled texture, and when it's stretched across large areas, such as a field of flowers. it can lead to unnatural repetition and an unrealistic appearance. Cell bombing splits a texture into multiple pieces and then offsets those pieces ever so slightly to essentially randomize the pattern of the material.
Hoj Dee has created a comprehensive tutorial on using cell bombing to effectively resolve the repetition issue when viewed from a distance while maintaining fine detail up close. Check out the tutorial above and watch his other Unreal Engine 5 videos: