i always trim to edge and add my binding. my binding is never the same as the back.
don't ask me why i don't know lol

It's personal preference. I find the 1/4 seam fills my binding.

I try not to overthink when it comes to quilting and I learned not to fret over how I make a quilt. I'll go by a rule of quilting until I decide I like my way better. Most quilting rules are outdated and not needed.

If I use 2.5"width binding, I leave a little bit of to fill in the binding.
If I use 2.25" width binding, I trim right to the edge.

This is exactly what I do... but I don't understand why you would do it any other way. I can't figure out the other methods you are talking about. Could someone snap a picture so I can see what you're talking about? I'm confused.

That only works if your intended finished binding is ¼". If you want a wider binding, and don't want to lose any part of your quilt top in the process, you must leave excess batting/backing extending beyond the edge of the quilted top. The amount that you leave will equal the desired finished width of the binding less the quater inch seam allowance included on the quilt top.

For example if you want a ½" binding, you'd leave ¼" of batting beyond the edge of the top. For a 5/8" binding, you'd trim the batting to 3/8" from the top's edge. Does that help explain it?

The easiest way to do it is to sew the binding onto the edge of the top as usual and then measure from that stitching line out onto the batting for the finished binding width you want and cut. The bulk of the batting/backing/seam allowances will add the necessary fullness and your front and back binding width will be the same.

ETA: Personally, I don't like ¼" bindings on much of anything, so I always leave extra batting. How much depends on the individual quilt. At my request, my longarmer does not trim anything at all.

The lady that longarms my quilts leaves everything on the quilt then I square up to the edge of quilt. Use the 2.5" binding folded in half, sew a 3/8" seam and fold over to the back and hand sew my binding. Have never had a problem with my binding not being full.

I don't leave any batting when I trim. I use a 2" strip for my binding and after it is folded in half then sewn with a 1/4" seam it fills the binding when I pull it to the back. If you are going to leave extra batting I would think that you would need to use more than a 1/4" seam

Here's a tutorial for a very exaggerated wide binding (5½" wide strips) that will clearly show how it works.
http://www.mccallsquilting.com/conte..._WEB_BONUS.pdf

If the seam at the edge of the quilt top is greater than ¼", you will lose part of the top...points, details, overall size, or anything else. There is no need for that to happen.

There are two discussions going on...the original about leaving ¼" of extra batting just to make the standard ¼" binding fuller and the secondary one about leaving extra batting to make wider bindings full without reducing the quilt top in any way.

Okay, I get it now. I guess I didn't think about having a binding wider than the 1/4" that I always do. Sometimes the brain just gets stuck on one idea.... pretty common at my age. I guess I need to broaden my ideas about bindings.