I use a leader to keep the thread tails controlled but not when chain piecing. I don't use one as a block unit. When the leader if full of thread I toss it. Any fabric scrap can be a leader. I like using a large piece of scrap so I don't keep losing it after snipping off.

I also stitch a 1/4” or so between pieces. It will be a chain stitch and I feel it helps secure the seam so it would be harder for it to unravel.

Thank you so much for clearing up the leaders and enders. I always thought that was a waste to put a small piece of fabric to sew before going onto the actual block you are making. Now I know if I am making something then I will just have a container of 2 1/2" squares right by my machine and away I go and it. Then you have two projects in a sense to do. Great idea and thank you wonderful members here.

I have sewn for more than 60 years and started using leaders about 10 years ago. The bigger the machine the more problems I seem to have with it pulling my fabric to the bobbin side. Older straight stitch machines don't have huge holes in the plate and were not much of a concern, but as machines got bigger and fancier, I have had to use leaders or I end up with a wonky corner when I start. I often use cut-up paper to get started rather than fabric pieces. I prefer the paper because I can keep little pieces cut up by the machine and they NEVER get pulled in.

I"ve never gotten the hang of them. and if used many times, how are they then used for a quilt. I'd have them full of threads...

I've always wondered about them as well. I like the idea of making 2.5 inch patches with them. Thanks for all who posted. I'm going to try this.

I think Bonnie Hunter is the queen of leaders and enders (at the very least a princess!) While it takes a little planning you can do a lot with her system.

Here's a link to her tutorial https://quiltville.blogspot.com/2005...-and-hows.html

I use triangles as leaders and enders so I end up with HST units. I usually pair a light with a dark or medium. I do triangles because it is easy to get a triangle out of an odd shaped scrap and before I got the Deb Tucker wing trimmer tool I made FG from a rectangle and two squares so I had lots of triangles from the cut offs. I have ziploc bags of HST that are 1 1/2", 1 3/4" and 2". Pretty sure I have enough of the smaller size to make a scrappy tree of life quilt.

There are two different strategies for leaders (and enders).
1) Use a scrap many times (usually until it is too full of thread to be used anymore), and then discarding it.
2) Deliberately plan to have fabric on hand cut and ready to piece to use as a leader/ender and then use this element in a quilt. (So this fabric is sown only once.)

So, if you're doing strategy 2, you might have a bunch of small squares on hand that you use when ever you are having a session of piecing. Let's say you sit down with your machine having nothing under the presser foot.
1) Get a clean start and piece two small squares together. To get the clean start, you can sew on a small scrap (to eventually be discarded) or hang onto your tails whiles you start on the squares.
2) As you finish the seam of the small squares, chain piece onto your "main" project. Keep chain piecing on the main project as much as you like.
3) As you finish your last seam on the main project piecing, grab another two small squares and chain piece onto them, sewing about half way down the seam. Cut the threads between the two small squares and the rest of chain piecing. Cut the threads between each of your chain piece elements, and set the two small squares used at the start aside for what ever project you will eventually put them in.
4) Go iron or do what ever you need to do ready for your next bit of piecing on your main project.
5) Come back to your machine and you already have your half sewn small squares under the presser foot to act as leader. Finish the seam on the squares and chain piece onto your main project.

So by planning ahead, you can always start and finish with the small squares, and avoid having to do (almost) any "cold" starts where you hang onto tails or use a scrap. As a bonus, you get a steadily growing pile of pieced items that you can use in another project.

If strategy 2 doesn't appeal, you can just adapt the above steps to work with two scraps and sewing half way down the second scrap as your ender, which gives you the similar thread savings of not having to do a "cold" start. When doing this, I like to have a handful of scraps near my machine, so that when I (temporarily) misplace one, I can just grab another one and not have to hunt for the missing one.

I learned how to chain stitch when I got my serger. That's what you do with a serger; put the next piece in as soon as the current piece is just past the needle. Then I took that to my garment sewing.
First I sew the two shoulder seams, one after the other, then the sleeves go on, then the side seams, all in one long sew. Some other things can be sandwiched in there also, as sewing the gathering stitches at the top of the sleeves in between the two shoulder seams; working on a collar or cuff at the end of any other seam. You can put a whole blouse together without ever pulling out and cutting the thread. That is really a thread saver and nothing gets jammed up.