I know a lot of people stabilize their quilts first, but I have done mine so far (only half a dozen quilts) without stabilizing. I have been working from left to right and then back right to left using a meander or looping all-over freehand design. I do make sure that my backing is square before loading. I have done three large quilts that way without a problem.
Have just read about measuring the width of a quilt as you go in order to make sure that the width does not change on you as you advance. Basically you just measure the width at the beginning, make a note of it, and then keep measuring as you advance. Measuring just means laying a long tape measure across the quilt.
When doing a separate border design (not all-over as I have been doing), I have read that a lot of quilters will do the top border and the bottom border plus the middle quilting, then take the quilt off the frame and re-load with the sides at top and bottom to do those borders.