A simple question but thinking about it maybe a good one!!
I used to get asked this question a lot some time ago. To those of experience it will seem second nature but the previous quote to me is quite correct. So what you may say.
The method stated may thinking about it actually be a bit pedantic, in fact the opposite technique may even be construed to be a another method of inducing slack line, which is not always a bad thing

. If you think of casting your fly like if you were firing a dart from an air gun, the straighest dart will have best chance of going where it's been aimed. Put a kink in the end of the dart and it will wiggle all over the place though. This for me may at least make you think about
why you may make your choice!!
Does anyone think this extra wiggle would apply to deep nymphs and so-on, say with a turle knot?
BC