Duplicate lines appear everywhere: copied keyword sets, merged email lists, stacked tags, exports from multiple sources, and checklist revisions. Cleaning them manually is slow and error-prone.
Keep original order
In many workflows, preserving the first appearance is more useful than sorting everything alphabetically. That makes it easier to review the final list against the original context.
Case sensitivity matters
Sometimes uppercase and lowercase should count as the same item. In other cases, they should remain separate. A good line cleaner should support both options.
Best practice
Trim spaces, decide whether case should be ignored, and review the cleaned output before using it in production systems.