A transmission line by dint of its design will develop a number of resonant modes throughout its length; it is critical that those modes be damped with stuffing or the response curve will be quite erratic. When properly stuffed a transmission line will have a smooth frequency response with no internal reflective modes and an impedance sweep will show a single impedance peak at the line frequency with no peaks anywhere else. Without adequate stiuffing it will exhibit numerous impedance peaks and the response will also be marred by a series of peaks and dips.