MSW

Hi i need some advice, my contractor installed my bottom kitchen cabinets and he did not use any screws and as mentioned he said that to minimise drillings and next time it will be easier to remove etc. basically the cabinets are placed on top of my concrete cement base and quartz top mounted and silicon over. is it done this way in this current era? will the cabinet toppled over? any issue with such installation methods? i need help seriously please give me all your expert advices? Thanks