They help resist cracking, crack growth, and chipping. These reinforced epoxies should not be confused with flake' or mica' additives which are sometimes added to low quality epoxies that have a permeability problem. These plates or flakes are intended to reduce permeability within the epoxy. A better epoxy is a wiser choice. Epoxy brittleness is a related topic.
Epoxies are naturally brittle.
Some epoxy vendors offer epoxies with flexibilizers blended into them. While the idea of a flexibilized epoxy sounds good, the real benefit of their use in rehabilitation projects has yet to be determined. What is new in the concrete coating industry is a group of products best described as water-based, zero thickness concrete sealers and fortifiers. Rather inexpensive, these single component products are rolled or sprayed upon exposed concrete where, like water, they quickly soak into the concrete. There they form tiny crystals inside the pore spaces along the surface of the concrete.