Sometimes teachers limit the opportunities they might give students to write simply because they don't have time to respond to every piece of writing. But please remember that sometimes the writing itself - simply having students think through an idea on paper - is the whole point of the activity. These writing-to-learn activities are geared toward students' needs - to articulate concepts they've just read or heard about, to critique a point of view, to clarify their thinking, to challenge an idea.
I've described a range of writing-to-learn activities elsewhere, but let me just note a few here:
Asking students at the end of a lecture to summarize the most important new idea presented in that lecture
Asking students to sketch the class for a student who missed class that day
Asking students "what most confused you in today's class?"
Each of these two-minute writing opportunities can help students learn. Teachers don't need to write responses to these kinds of writing.
That's not to say that you might not want to read this writing. Skimming through a set of responses to "what most confused you in today's class?" could help you plan the next class session. You might even want to refer to students' writing as you clarify or elaborate on points in a subsequent class. But you don't always have to spend time responding to every piece of writing students turn in.