Observation logs are a great way to keep detailed and organized records of your observing sessions. By recording your observations, you are likely to spend more time exploring an object and will ultimately see more detail. This is particularly true if you make a sketch of the object.
By having a record of past observations, you can compare how an object looked using different eyepieces, magnification, filters, barlows, telescopes, and other accessories. It provides you with a list of which eyepiece and magnification works best on a particular object and whether a particular accessory such as a filter helps to bring out detail.
By making a note of the atmospheric turbulence, you soon learn which objects can and cannot be seen clearly under particular atmospheric conditions. When making an observing list, you will be able to choose those objects that are appropriate or inappropriate for the current atmospheric conditions. For example, atmospheric conditions might be fine for planetary observing but not for deep-sky observing.
If you are one those amateur astronomers lucky enough to discover a new comet of supernova, your log will offer an indispensable way of substantiating your claim.
But even if you never become famous, a logbook is a great way to evoke memories of past observations during those long cloudy nights.
Suggested Reading
The following is a list of astronomy books that can help you with your stargazing.
Starlight Nights: The Adventures of a Star-gazer by Leslie C. Peltier.
Stargazing: Astronomy without a Telescope by Patrick Moore.
Nightwatch by Terence Dickinson.
40 Nights to Knowing the Sky by Fred Schaaf.
Secrets of the Night Sky: The Most Amazing Things in the Universe You Can See with the Naked Eye by Bob Berman.
Skywatching by David H. Levy.
The Stars: A New Way to See Them by Hans Augusto Rey.
Exploring the Night Sky with Binoculars by Patrick Moore.
Stargazing with Binoculars & Telescopes by John Mosley.
Exploring the Night Sky with Binoculars by David Chandler.
Binocular Astronomy by Craig Crossen and Wil Tirion.
How to Choose Binoculars by Alan R. Hale.
Touring the Universe through Binoculars by Phillip S. Harrington.
Starware by Phillip S. Harrington.
Astronomy with Small Telescopes Up to 5 inch, 125 mm by Stephen F. Tonkin.
The Cambridge Guide to Stargazing with your Telescope by Robin Scagell.
Telescopes and Techniques by C.R. Kitchin.
How to Use an Astronomical Telescope by James Muirden.