Sometimes. As concrete hardens, or hydrates, it develops internal stresses which may cause random cracks. In the Midwest, with our annual freeze and thaw cycles, your outdoor slab is constantly in motion. If the slab is installed correctly, using high quality concrete, good soil prep, proper rebar installation, proper control joint placement, and correct curing methods, we can limit the possibilities of cracking. Though it is not guaranteed, decorative joints are cut to relieve stresses before they form random cracks.