I vehemently disagree with this saying (just as I do its twin sister, "anything goes") when generally applied. But it's useful in narrow scope, such as spinning. In other words, use what you love, and remember, there are no spinning police! Case in point:
I've almost filled another bobbin with my marled two-ply, but ran out of spun Shetland. So I whipped out my Jenkins standard Turkish spindle to spin up the last of Braveheart's roving to ply with the remaining Jacob. I love the juxtaposition of new and old technology, both executed in beautiful woods, and both doing their jobs so well. Here's a close-up of the myrtlewood spindle's whorls; so, so pretty:
The first skein of marled yarn came out noticeably bulkier than this second bobbinful, so I don't think I'll be able to use them for the same project. Disappointing; I obviously need to get better at spinning a consistent single.
That's it for now from . . .