The major result of demobilization was an increase in unemployment. As the men came back, they were looking for jobs, but the country was in a bit of a recession and there were not enough jobs to go around.
The men who had gone off to war came back and could not find jobs. Their jobs had not been protected when they went off to fight in the war. This meant that they had to look for new work and could often not find it because the economy was in a slump.
It appears to me that the picture of unemployment and recession painted in the answer above is rather exaggerated. Except for two short periods temporary recession, first one starting in last quarter of 1918 and ending in first quarter of 1919, and the second one in 1920, the American economy experienced an unprecedented boom in 1920's.
I have no published reference to support my view, but I do consider it highly improbable that American soldiers returning to their homes after the World War I, were immediately thrown out of army, turning them into unemployed persons seeking jobs. I am sure that these people must have been honourably discharged from the army with handsome rewards and perhaps some pension. Also these soldiers must be having lot of accumulated savings in absence of opportunities to spend their earnings on war fronts. Under these conditions, I am sure the that they had enough money to spend for enjoying their life after returning from a long war. and this spending must have contributed to the economy to the boom of 1920's after World War I. And I am sure ex-American soldiers must have found enough jobs once they really needed them in 1920's.