each person has their own specific position or job with no redundancy; one-to-one allocation of personnel to tasks

公司现在是一个萝卜一个坑，每个人都忙得不可开交。

each person or thing has its own specific place or partner; a proper match for every situation

找对象这种事，一个萝卜一个坑，总会遇到合适的。