Usually I shut down my MBP when I go to sleep because I don’t really like the idea of having it connected to the power supply while I sleep after my battery died under very suspicious circumstances. By default the MBP goes to sleep mode when you close the lid (suspend to RAM), but if it’s not connected to a power supply that obviously consumes some energy from the battery.
When I changed its sleep habits to
hibernatemode 1, the MBP does suspend to disk (it saves the content of the memory to the hard disk). It needs a little more time to wake up (compared to suspend to RAM), but now I can sleep without worrying about exploding batteries and return to where I left my work the next morning.