Lost loads of progress because you never though Unity would crash while saving your scene? Well let me tell you, it happend to me... but not anymore thanks to SCENE SAVER!
Scene Saver is a handly tool that creates backups at points where things could go wrong. Once you've set up your preferences, everything is out of your hands and you wouldn't even know it's there! Then, when things go wrong, you can go to the backup folder and use any of the scene backups place there.