A statistics pass reports the basic dimensions of a text: how many lines, how many words, how many characters.
The value of counting first
Before processing a list it is worth knowing its size, and after processing it is worth knowing whether the size changed as expected. A filter that was meant to remove a handful of rows and removed half of them has gone wrong, and the count is what reveals it.
Comparing before and after
The difference between two counts is a check on every list operation. Deduplication that removes nothing means the list was already clean, or the comparison rule was wrong.
Where it fits
Run it at the start to know what you have, and after any step whose effect you cannot see at a glance.
Try it: Line & Word Statistics Counter on SeoWolf's Notepad.