A centralised SOW should be like an iPhone (when they first came out, and they were miles ahead of all other smartphones, and shiny and beautiful). A SOW, like an iPhone, should be designed by someone who had the time to put a lot of thought into it, proofread it, and maybe show it to a colleague to see what they think. Then, once it is a polished, finished product, and sent out into the big bad world to meet the students/consumers, it should work really, really well. It should perform its function so well (getting the students to learn new things and acquire new skills) that it is a joy to use as a result – it does what it’s supposed to do with such incredible ease.
Lessons being planned the night before by a teacher is perhaps comparable to your shoelace breaking, and you having to improvise a shoelace out of a bit of string. You’ve done it hurriedly, because you need to get your shoe on and get out to work. It will look a bit shoddy. To be sure, it will do the job, but not very well (it might come undone frequently, for example). Most of the time, you won’t notice how substandard it is, but when you get around to buying a proper shoelace, you will be relieved.