Double digging or new soil?

[Farmette]

Will be helping someone to create 8 raised (2" x 6" lumber) beds that are 4 by 10 ft. In the past, I have purchased a large amount of planting mix to fill my raised beds and it has worked very well. Recently someone suggested "double digging" when preparing thesebeds as a means to achieve biodiversity in the soil. If anyone here has experience with both methods and can speak in favor of one or the other, I would appreciate your opinion.
Thanks
Chris

[huntoften]

When I build a new bed, I use my mantis tiller and till down around 6-10 inches, then I put a 6 inch layer of compost along a few shovels of perlite and a few shovels of vermiculite on top of that and till it again. I then plant it and use it for one year. The following year, I add another 4-6 inches of compost on top and use my garden claw to work it in. From then on, I add a inch or two of compost each year depending on the level of the bed and never till it again. Just make sure you never step in the beds to compact the soil and it will stay fluffy and light and produce very well.