There is social pressure at my school for two mutually exclusive, yet very important, elements in lesson plans: 1.) a classroom experience which places a premium on teacher/student relationships and in-class experience, and 2.) portability of lessons, so students can re-learn standards and make up assessments in places other than the classroom.
The first is important for several reasons. One reason is sort of a justification for the continued existence of brick-and-mortar schools: if a student could take what they're doing in your classroom and do it anywhere, then why does s/he need to go to school? The converse seems like it would be a good argument against brick-and-mortar schools: Students shouldn't have to go to public schools; anything they can learn there, they can learn with their iPods and computers at home. Put another way, I don't have to stay here to do worksheets, I can do worksheets at the beach! (I can't cite a source where I've seen this argument. But it doesn't seem like the sort of thing I'd come up with on my own. I suspect the Mackinac Center, but then I blame them for everything*.) To be clear, I'm very pro-brick-and-mortar-school, and I'm very pro-technology-in-education. In addition, I think it's just a sign of respect towards the students that you're going to use their time efficiently.
Another reason for good, high-quality experiences in the classroom is that a much higher-quality educational experience can occur in the classroom. We teachers are supposed to be experts in edcuation, by which I mean we can do better than pass out "match-the-word-to-the-picture-it-describes" worksheets, sit back, and watch the "learning" occur. With the time we have our students in class--with all its flaws, with all the interruptions, with all the classroom management difficulties and personality-conflict issues and apparent student apathy, the experience we can give to students while they're in our presence is better in every way than the one they can get without us--it should be broader, wider, and deeper than the experience they get by bouncing YouTube videos back and forth to each other. I'm not downing on technology, of course. But technology is most effective (educationally speaking) when it's coordinated with other technology and real life (not controlled, coordinated) by an intelligent, aware adult with an eye on long-term learning objectives. And even then, there's a lot that can't be learned on the computer outside of the classroom.
On the other side, a certain amount of portability in lessons is necessary. Students are absent; they have to go to the office; you go to a conference and leave a substitute who almost certainly knows nothing about your subject (regardless of what your subject is); you have to work lessons around Picture Day and the Halloween Costume Parade. Occasionally, they spend time in in-school suspension. During these times, a packet of papers that students can take with them and interact with the lesson in a less real-time way becomes much more attractive, to teacher and student. I get frustrated when I spend a long, productive day full of kinesthetic learning activities that students seem to enjoy, and the next day another student comes up and says, "What did we do yesterday? My mom needed help frosting cupcakes." (Or I was on my death-bed with strep throat. Whatever.) It seems really lame to say, "Remember the vocab sheet I gave you on Tuesday? That's what we did." ¿Meh?
Also, if a student doesn't understand a lesson the first time you teach it, it's not going to do a whole lot of good to simply repeat the way you did it. So you need to have a backup plan. So twice, I've now come up with a reason for having more than one lesson plan--one, full of classroom-intense, socially- and emotionally-rich lesson plans, another that has students teaching themselves your material somehow. *Sigh* The good news is that most textbook companies already have the second lessons covered.
*This is tongue-in-cheek. I'm willing to listen to any idea that supports education that the Mackinac Center for Public Policy comes up with. As soon as they have one, I'm sure someone will let me know.