This arranges lines in ascending alphabetical order.
The most common list operation there is
Sorting makes a list navigable, brings identical entries together, and is a prerequisite for several comparison operations that assume ordered input.
Duplicates become visible
Once sorted, repeats sit adjacent. Even without running a deduplication pass, a sorted list shows you how much repetition it contains.
Numbers need a different sort
Alphabetical ordering compares character by character, so 100 sorts before 99. Anything numeric requires a numeric sort instead.
Try it: Sort A to Z on SeoWolf's Notepad.