The sheetbend knot is very similar to the lap knot (castwell knot).

Does anyone know if makes any difference in the effectiveness of the knot for securing a looped leader to a fly line?

This page shows both the sheet bend and the lap knot

http://www.realknots.com/knots/sheetb.htm#Xschootsteek

I ask because the Sheet bend seems to be a knot still in my memory from my boy scout days a few decades ago. My mine wants to tie it instead of the lap knot.