I've been thinking, lately, about the things one can wing.
The list of Things Wingable probably varies by individual, but I suspect that everyone's list grows with age--as we develop more confidence and a greater store of knowledge (of our subject area, of our audience, of ourselves). Still, I feel comfortable asserting the following:
All performances may be winged (or, following Dr. Virago, wung). Thus a class, a meeting, or conceivably even a talk--though your Flavia is not remotely expert enough for that last one and suspects she never will be. Anything done live and leaving no permanent record can be carried off without a great deal of formal preparation if one has enough charm and bravado.
Written things cannot be winged. They're permanent. They should reflect, if not careful thinking, then at least careful writing. Those things take time, and although time alone doesn't guarantee that they'll be good, writing can't be faked in the same way that a one-off performance can be.
Grading also cannot be winged, and for the same reasons.
Administrative tasks, alas, also cannot be winged. They require paperwork, meetings, paperwork, email exchanges, paperwork, phone calls, and more paperwork. And while writing can be almost infinitely deferred, paperwork WILL NOT BE IGNORED.
So, when something has to give, you know what it is. I've been winging a lot of classes lately, and I hate it. I hate the fact that, because I have forms and applications and committee work with absolute deadlines, I come into the office, spend four hours on that stuff, read or skim the books I'm teaching the next day, and show up in the classroom without more than a few dogeared pages to guide me.
I've also been doing precious little writing, here or elsewhere. But I'll tell ya: getting paperwork in on time? Returning students' papers promptly? That's all you need to do to aquire a(n entirely undeserved) reputation for efficiency.