And finally, these perfect pieces are being sold at a higher price because they look best (and you are therefore making them Grade 1), not because you are determining that they perform better dynamically due to the way they look. You could make an equally performing table from the cheaper wood.
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Yes in fact a board with no knots will be unlikely to split when dried, also it will be able to be worked however the maker wants it and will be a stronger longer lasting bit of furniture.
And as for heartwood, I understand that it is stronger, maybe a little more brittle but should have greater strength.
I'm not sure about what people call Butterfly, I've see all sorts of knots called it, but I guess as with everything the seller will dress his/her product as they see fit, in order to boost sales. You get all sorts of stain in wood, none really affect it other than cosmetically.