In reply to Jon Dittman:
I'm relatively new at this game, but I read in a Jingo book that you need a *minimum* of 10cm slack (approx 4inch) at the end of a fig 8, "In a shocking fall, a knot will easily tighten and pull through around 100mm".
Perhaps stoppers are there to ensure you have at least this amount of slack...it takes more than 10cm slack to tie one (gets the ruler out)?
Ah, reading earlier in the same book..."Often a small stopper knot is used to tie up this loose end, but it is of no stength or significant importance. It does however add safety for a beginner in that you need around 30cm to tie the stopper and thereby alerts you if you have forgotten to leave a good end".
Dunno - I don't necessarily believe everything I read in books but include here for (non-flaming) comment