As said above. The middle position of a triple is in the middle of the chain line with the inner and outer set 5mm either side.
A double has the inner and outer 5mm apart but set either side of the midline, ie +/- 2.5mm. So if you run your single ring on the outer of a double spider, your chain line on the inner cogs is suboptimal. Not disastrously, but sub.
You can compensate by moving a 2.5mm spacer from the drive to non drive side of the bb – then your chain line is back in the middle but you cranks are offset. But you’ll never notice. Or, I have heard you can space the chain ring back in with spacers.
Lastly, I believe (never proven, just musings) that the way that these nw rings work, with the teeth being a tight tolerance to the chain inner plates, means that when at extremes of crossing there is more interference with the chain leaving the chainring, whereas on a normal ring there’s a bit more space for the chain to run at an angle before it starts to rub on the chain ring’s teeth. Hence noisier and more prone to unshipping when you back pedal.