If you don't disable Fast Startup on a dual-boot machine, "shutting down" Windows does not leave the disks in a clean state to be accessed from your other OS (Ubuntu in my case). It goes into some sort of deep hibernation with the disks still "mounted".
I haven't done any formal tests, but it doesn't feel any slower booting up without Fast Startup.
And of course, +5 for the tip. I'd found it, but it took a lot of digging, with considerable help from Dr Google's interns.
Software rusts. Simon Stephenson, ca 1994. So does this signature. me, 2012