I use a leader all the time with one of my machines. Likes to stall up and stich over and over in the same spot or sometimes pull the fabric into the plate. Makes me crazy when I forget. That ususally happens when I change machines.

Usually only if I'm piecing triangles and for some reason must start on the pointy end. Otherwise just holding my threads seems to work for me.

Always....it keeps my thread taut, no thread bunching on the bottom... but most of all it saves thread. Have you ever saves all those long threads you pull as you start piecing. You would be surprized. They make quite a pile.
I call that little scrap my "start & stop".
I start off with it, cut it off and it is the last piece to go under the foot before I stop.

Almost always. Sometimes it's not possible when paper piecing since the sewing starts in the middle of the paper, and I miss having the leader then.

never

Always,..... even with paper piecing I use a leader.

Never. I just put my finger on the threads so they don't bunch.

Almost always.

I always use a leader. It saves so much thread.

Started to use them when I heard about them on this site. Saves on a lot thread and I like it better than holding the thread. Someday I hope to be organized enough to piece squares.