The columns are long and slender structure & most of the time concrete is planned upto 2.4m height in single pour. The IS recommendation states that the concrete height should not be more than 1.5 metre, Segregation of coarse aggregate might take place if the height of pour is more than 1.5 metre. To avoid segregation fresh (green) concrete after placing is vibrated.
What if you dont vibrate a Column?
There is chance of honey comb formation in column. Which adversely affects the functionality of the column.