Lines on side of the print

The aim of every print is that the surface comes smooth layer by layer. If one of the layers goes wrong, it is clearly visible at the outside of the object. For example: one layer of ten is wider than the others.
The consistent diameter of the filament plays a big role and an exact positioning of your axis could lead to lines on the surface (e.g.: z-wobbeling). A bad tuned PID controller would be another reason why these lines appear. In this case the heating of the nozzle is inconsistent.