I serge around the raw edges of material before I wash it. Just recently I got some fabric from someone that apparently a cat laid on. I serged around and thru it in the washer. Cuts down on the raveling big time. I prefer not to wash my fabrics before quilting, but sometimes you gotta!
I use my sergers for many things. Made a pillowcase for a quilt to be given with the quilt. Serged the raw edges.
My neighbor made a quilted table runner with her serger. I have a neat pattern for a serged quilt I hope to get to someday. If I was only quilting, I wouldn't see the need but I also make other things. Baby items, mending and such.