Most of the time I bury them as I go. It doesn't take long and it prevents having those pesky tails to avoid while quilting. I pull the bobbin thread to the top, knot and then bury. I do this for my larger wall hanging quilts and also for ones that will be used as quilts. If I think the quilt will get heavy use and lots of laundering, then I take tiny stitches at beginning and end, but still knot and bury both starting and ending tails.
For my smaller art quilts that are mounted on panel, I take tiny stitches to start and also tiny stitches to end, then use the automatic thread cutter on my machine. These quilts are glued to the panel, so the back is not visible, and the glueing prevents the unburied threads on the back from coming loose.
Rob