I know a lady who serges the quilt top - she's had issues where the stitching on pieced borders has spread or broken while the quilt was being handled (before being finished). This reinforces that edge and the results aren't seen since serging is less than 1/4 inch. I doubt she does it on a regular one fabric border quilt.
I also know someone who serges the quilt sandwich before putting it on to quilt - she only does this for kid quilts though. You don't generally have the wavy border issue on a small quilt, so I can't see a problem with it. I know it's easier to attach the binding if the edges have either been serged or sewn down first. I did it once - I would do it again for a high loft batt, but not the typical low loft most of us use.