I do quilt with a longarm and will use a sheet if that is what my customer brings to me.I nor my machine has a problem with using a sheet. However, that said, the higher thread count of the sheet will sometimes leave a poor looking back as the quilting stitches look as if they cut the threads of the sheet instead of finding space between threads and sinking into the batting. If a person wants to use a sheet I would recommend one that has been washed several times to soften it up as much as possible.