Hi Sandy:
I agree student expect their teacher to know their subject well. But even good teachers who don't plan well, are not prepared, appear busy and disorganized will send the wrong message to their students.
It pays to plan time in preparation. That class that runs seamlessly from topic to topic, all resources aligned, teaching aids, ready - that demonstrates readiness, and students admire and appreciate their teachers that take the time to prepare.
Regards, Barry