For each increment of zero filling, the number of data points defining a line shape is increased. The trade-off is the size of the FID increases proportionately. An FID with 1K = 1024 points will produce a file of ~ 50 kb (including data parameters). The goal is to balance the file size with the amount of gain from applying zero filling.
Spectra A and B appeal aesthetically due to the higher level of smoothness across the signals. Whereas the original data, spectrum E, is jagged and presents less than ideal line shapes.
Analysts typically apply 1 to 2 zero fillings; this equates to adding respectively 1 to 2 increments of zeroes equal to the number of data points.