Care to expand on that?
The knot weakens a rope, depending on how it 'grips' the rope it is tied in will dictate by how much. Some knots are better than others, I got a book from the library once 
It quoted a bowline knotted rope as having 45-50% of it's original strength. Some knots only reduce the strength by 10-15%. Ashley Book Of Knots (ABOK#) being the standard ref. Can't remember the name of the book I read on the subject. I use bowlines for the ease of un-tying but for certain applications and rope diameters have changed to the what I thought was a fishermans knot but it isn't like the ones above. Closest I see to the one I tie is the perfection knot.
