Knowing the line number in Vim is crucial: you might need to jump to a specific line to fix a compiler error, you might want to check your current line to tell someone else where they broke something, or you might need to know a line number, and the diff to your current line, so you can delete N lines.
You can "set number" to get the line number in a bar at the left, and that's fine for most things but also quite unnecessary:
- You can jump to a line by typing ":"
- You can see your current line by checking it on the lower right status box
- ... but what if you need a delta from your current position?
That's even easier: just "set relativenumber" and the numbers on the left will turn into a relative position from the position of your cursor.
Now you won't have to count the lines you want to delete: you can instantly know the N on dNd!
Bonus: watch vim newies struggle with the changing line numbers