Burning unseasoned, green, or wet wood will cause the fire to smoke and smolder more. Lighting it can be brutally difficult and that should tell you that it probably shouldn’t be burned. When this is ignored, burning wood that is unseasoned will allow for the build-up of creosote in your chimney. 

The "smoke" of unseasoned wood is heavily laden with unburned creosote. Because unseasoned wood causes the whole system to burn cool, the creosote laden flue gas [smoke] quickly condenses on the surface of the flue.

Effects of creosote is the largest danger that burning firewood can create and it is a result of negligent maintenance of firewood burning system and the use of wet wood. It tends to clog the exhaust and cause the particles to re-enter the home.

Creosote is a flammable, tarlike material that collects inside the chimney if its components aren’t burned off inside the stove. Creosote can cause your home heating system to have very ineffective exhaust. Creosote builds up inside the chimney and restricts the exhaust from exiting your home. Even worse, Creosote is very flammable and can cause chimney fires which can be simple, small and unnoticed, or they can erupt and devastate your chimney and home.