There were two main purposes for General William T. Sherman’s “March to the Sea” through Georgia. One was a traditional military purpose while the other was more of a “total war” purpose.
Total war is a term that refers to conflict in which all parts of a society are seen as fair game. Armies do not simply attack other armies or military objectives. Instead, they do things like destroying civilian infrastructure that could be used to support the enemy’s war effort. In Sherman’s case, the goal was to wreck everything in his path so it could not be used to help the Confederate army. For this reason, he destroyed railroad tracks and factories and either consumed or destroyed crops.
There was also a more traditional military aspect to the march. General Robert E. Lee of the Confederacy was under siege in Virginia. If Sherman marched to the sea, he could turn up the coast and put more pressure on Lee. At the very least, he could occupy Southern troops that might otherwise come to try to lift the siege of Lee.