Toy covers and condoms are used to help make cleanup easier, to prevent the possible transmission of STD/STIs, to prevent cross contaminiation if you go anal -> vaginal (change it after anal and before vaginal), or to protect your body from toys made from non bodysafe materials. If you use bodysafe, nonporous materials (silicone, glass, metal, etc.) and wash between uses/ sanitize between people and anal/vaginal use you don't need them and they would merely be for convienience. less