Ask any teacher why they come to school sick and you will usually get this answer, "It is harder for me to have a sub, than to just come in." Personally, I rarely ever take a sick day when I am sick unless I can't stand up. One time I couldn't talk, so I typed to my students on the overhead when I needed to tell them something. Most students are really understanding when the teacher doesn't feel well.
The amount of work is usually double for any teacher who has to be out. First there is the detailed sub plan. Here the teacher has two choices, create something that goes along with the current unit plans so you don't fall too far behind or pull out the plans you hopefully made at the beginning of the year that have nothing to do with what you are currently teaching which throws you at least a day behind (then if you use this now you won't have it later when something else has happened or your even sicker so you will have to come up with an additional plan in the middle of your normal work).
Whichever option the teacher chooses, all that work has to be graded be cause if you don't grade it then the next time your out the students won't take the sub assignments seriously which lead to a bad day for the sub and a long note for the teacher to read the next day.
If students have have their own devices, the narrative changes. The activities for the day can be posted to the teacher's online learning management system. Videos can replace lectures, reading can be assigned and discussed through collaborative documents or blogs, and assignments can be turned in and ready to grade without having to be picked up from the school or can even be graded automatically if it is set up in the right way. This method would seem more meaningful than review worksheets or silent reading and writing assignments. These tasks can review skills, but the social aspect of the learning is lost.