Found the above video while looking for reference and I think is among the best produced yet.
I could think of a few reasons why you would want to tie your own tapered leader.
- Cost saving – By using mono you save considerably compared to buying manufactured tapered leaders of the shelf
- Flexibility – ability to control length and breaking strength
- Allows for ease of changing tippet quickly through loop to loop connection
- Some fly fishers believe the DIY leaders actually unfurl (present) the fly better