It's all about having a good match. Knotless leaders are the generic, catch-all leaders that will serve a wide variety of applications fairly well. Knotted leaders are often built for a specific application.
A knotted leader's individual sections can be fine tuned, by altering the length and thickness of each section. This means a person can build a leader to suit a specific application. You can't generally get that with a knotless leader. Yes, it might be painful to do all that experimentation, but there are lots of talented leader makers out there, and they've pretty much done the bulk of the homework for you.
Get on a search engine and search for Leadercalc. It's an Excel spreadsheet that has a wealth of information on knotted leaders. That should give you an idea of the variability and what works for certain circumstances.
---------- Post added at 12:49 PM ---------- Previous post was at 11:19 AM ----------
Originally Posted by FrankB2
I don't own a precision micrometer, but would love to run one along the length of a few "identical" tapered leaders.
Before I stumbled onto Leadercalc, I wanted to tie a knotted leader with similar specs to a knotless leader that I liked, so I did a little bit of experimentation with a dial caliper a few years back. Most leaders weren't too far off, certainly less than .001" at any given point along their lengths, provided I compared leaders of the same brand and model, but differences between brands were absolutely unreal. As I recall, the main difference was in the length of the butt section. In 9 foot leaders, there might be a foot or more difference between the lengths of butt sections.