There are some projects that just don't work well with Leaders & Enders for me.
Any paper piecing project where the seams are short and in the center of the paper template make it really hard to chain anything without a complete and utter waste of thread (and time) so Leaders & Enders take a back seat there.
That also applies to things like string piecing where I can use the units themselves as Leaders & Enders and just work on two blocks at a time - one engine, one caboose - trimming my work off from behind the presser foot. I complete two blocks, and when one is done (or both) just pull in a new foundation and start on the next ones.
When I piece on paper the stitch length is set smaller, and I just don't like to work on a second Leader & Ender project at that point.