As a teacher, I have never expected a substitute to teach what I would. It may take a teacher an extra hour (more or less), outside of the school day, to plan for his/her day off. At times, this is done while pressing through a restrictive illness or bereavement of a loved one. It accompanies the guilty feeling that the teacher is abandoning a classroom full of students who need him/her. It is done with the understanding that a substitute may not be available, students may be distributed into other classrooms, and the plans may be of no use after all. And the day off may actually be spent, not only recovering, but also in planning, grading, or studying data and educational research.
When administrators, legislators, students, parents, peers, patrons, or passersby think teachers are lazy or avoid work, they are mistaken.