It depends on the thread. Cotton will not unravel, poly will. I use poly 99% of the time and I leave about 1/4" at the end of a seam. I dont think it matters if it unravels once the quilt is finished but I dont want it unraveling while Im still working on the quilt. Leaving the 1/4" insures that it wont unravel beyond at least until Im finished piecing. Also when Im finished piecing I sew all the way around the edge with about 1/8". This keeps outside edges from popping during the quilting process.