The rationale for having the feed dogs up and stitch length set to zero is that when the machine is "making a stitch" the feed dogs grip the sandwich by coming up to compress it. This is supposed to make a better stitch.
Because the stitch length is at zero, the sandwich isn't moved. I don't see that this would wear the feed dogs down or have a negative impact on the Supreme Slider (or substitute) because it's just touching it, not pulling it.
But as always, experiment and do what works for you!

Brilliant idea! Thank you!

On my Janome 6600. I follow Leah Days advice and keep feed dogs up. I don’t use a supreme slider. It’s easier to make my stitches even

I have a sit down longarm, sweet 16 and of course there are no feed dogs. I have a little more trouble keeping the stitches even.

I keep my feed dogs up and the stitch length set to zero. (last 10 years) I learned this setting option for free motion from Leah Day. I have found with my stitch length set to zero, my feed dogs do not move, so my supreme slider is not damaged. Every machine is different, so make a practice quilt sandwich and try your machine both ways...feed dogs up / feed dogs down. Both options work so it's up to you to decide which option gives you the best stitch quality.

I wonder why the option of feed dogs or no feed dogs on the machine if it wasn't for a specific purpose. It is extra expense for the manufacturer and if was unnecessary it would't be on it or it's considered an expected feature that adds to the cost of the machine.

I quilt with a Janome 7700. I tried both, feed dogs dropped and feed dogs up with 0 stitch length. For me, my stitching was demonstrably better with the feed dogs dropped. So that is what I do on that machine. But if I changed machines, I would be sure to test out both methods to see which worked better for me.

I have heard some quilters leave dogs up, but it seems like keeping them up would inhibit all the multiple directions and organic movements you want to do with FMQ.

it would seem that way but for me it doesn’t. I think the result is better on my machine. Brother PQ1500

I have a Juki 2010. I have done it both ways. Sometimes I get better results with feed dogs up and 0 stitch length and sometimes with feed dogs down and set to 0. No right or wrong way if it is working for you. The feed dogs do not move with 0 length. If they did you wouldn't get a 0 stitch length.

Back in the day, people used hoops to do embroidery work on garments, and to darn items, so they needed to be able to drop the feed dogs. I think that the cost of retooling the factories and redesigning the machine far outweighs any benefits to a manufacturer so they just leave well enough alone.