On Tue, 15 Dec 2015 13:20:02 -0800 (PST),
wrote:

When/whatfor does one use a sheet bend, vs. a square knot?

You use a square knot (or a surgeon's knot) when you want to pull the
line tight while tying it, as when tying your shoes, tying a package,
or (so I have been told) when reefing a sail.

You use a sheet bend (or some other bend) when you want to tie two
lines end-to-end. The square knot isn't suitable if the two lines
don't match, it may jam and be impossible to untie, and it's apt to
capsize into two half hitches when wooled around.

But when I want to tie two threads together, I generally just hold
them together and tie a half hitch in the ends. It holds, and I never
meant to untie it anyway. It does make the thread more likely to
break when pulled, so I'd never use this technique on rope.

And I'll confess to using a square knot on cord elastic. When pulled
firmly, the elastic deforms permanently, so *any* knot will hold. (But
if I have to open a seam to re-tie elastic that's come undone, I use a
sheet bend.)

--
Joy Beeson
joy beeson at comcast dot net
http://wlweather.net/PAGEJOY/