i activate it to show when i take a pic, but mostly i would just view it to see if there is any skew, like if there is more overexpose or underexpose. but do not that, if your pic is generally more white or more dark, your histogram is not a good indication of exposure.
The mountain means most of the pixels are at that grey point. In the middle probably means that the shot is balance but not always correctly exposed. But most likely that will keep you most details for highlight and shadows for you to do adjustment later on.