I shut down my laptop every night, and I used to unplug the AC power as well when I shut down. Is there any harm to leaving the power brick plugged in while the laptop is off? Am I wasting energy? Am I causing harm to the battery (which I pretty much leave in all the time)?
If the 'power brick' gets warm when it's plugged in even when the computer is off, it certainly is using power, but maybe not much.
I tend to switch off computers, and unplug them, because I'm concerned about damage from electrical storms. I've lost a computer that way before, so I'm probably over-cautious.
I'm not sure whether modern batteries suffer from being continually charged. It depends on the type of battery.
On the other hand, electronic equipment is more likely to fail during the application of power, because of stresses induced by transients. I'm just talking about normal transients, not 'surges' or 'spikes'.
So, there are 'good' arguments for both turning 'em off and leaving 'em on.
I might add that I tend to check the likelihood of overnight electrical storms, and then leave the computer running anyway. There's always something it could be doing.
IIRC, if you rarely use the laptop on battery power, it may be beneficial to cycle it at least once a month, if for no other reason than to help maintain an accurate capacity reading. In addition, there are some cases in which extra heat on the battery can lead to deterioration over the long term, so it may be beneficial not to leave it plugged in and powered all the time (ymmv).
The best place for info on batteries in general, and LiIon laptop batteries in particular, is Battery University.