I trim mine first. I have even sewed the binding on just the top before sandwiching it, but this only works with machine or handquilting it. That's the way my DM taught me and she's quilted for many,many, many yrs. and there's NO quilt police!

I trim mine. I use 3" binding. I need to see the edge so I can test wrap the binding so make sure it will wrap to the seam line.

I used to trim mine, then sew on the binding with a 1/4" seam. However, now I square up the quilt first and mark the squared-up line with a Sharpie permanent marker. Usually I do a fairly big zigzag stitch outside the marked line to stabilize the edge, then rough-cut outside the zigzagging. The marked line clearly shows the edge of the quilt, so I line up the cut edges of the binding with the Sharpie line and sew the binding on.

Only after the binding is sewn on do I cut the excess batting and fabric away. Before I cut, I pull the binding over to make sure the binding will be filled. This allows me to make any minor adjustment in the 1/4" seam allowance so that the binding folds over the edge perfectly.

This system works really well for me.

I trim first,about 2" from the edge.

I trim first,as well it just reduces the bulk.

Because I quilt right up to within 1/8" of the quilt top edges, my edges are secure and then I trim my backing and batting before I sew on the bindings.

I always sew the binging on first and trim with the rotary cutter so that it is nice and straight.

I try to have about 2-3 inches overshoot of both backing and batting prior to quilting in case there's shifting while quilting. I leave it during binding and then use a good old-fashined pair of Fiskars sheers to trim backing/binding to 1/4 inch binding seam. Works for me!

I stitch 1/8" in on top all around, trim excess batting and backing away, then attach binding to front and turn to the back and bind.

Thanks everyone for your replies. I appreciate all the help and suggestions.