I've got clay pipe, but it's under my (perfect) concrete driveway. So, I bite the bullet and snake the roots out about once a year. Oddly, every February.
Our city had a company line their mains with a resin impregnated sock. I don't think too highly of it. I had to snake my line a week after they were done and my snake pulled back an awful lot of plastic resin stuck to it. Looked like a bunch of brillo pads. (I snaked to the main.) I think I scraped it off their pipe. Oops!
I used to use copper sulfate crystals (from an agricultural supplier is way cheaper than in the little hardware store jugs). I'd apply it on the same day I augered the line, so the little root fibers that remained were wounded, thus open to leach in the copper. Then again every 3 months. When I did this I'd go more than 2 years between snaking.
But, Coper Sulfate may eventually kill the tree. It also is harmful to any fish or plants or frogs in ponds and stuff, if it hits the water. It's used to kill algae in ponds and cooling towers and brine shrimp in rice fields. Detroit? Rice Fields?- OK- I read that one on the bag. Veggies hate copper. Animals need (& can only tolerate) a very little. - Look at a vitamin bottle for how small the dose is. I stopped using copper sulfate on the drain.
However, once I had to cut down a diseased tree. I ignored the stump. Roots kept growing and shoots would grow up all around the stump. To kill the roots- I shined up a chunk of copper electrical bus and drove it into the center of the stump. I left it over winter. No more roots or pop-up shoots. (That reminds me- dig up the stump. Oh well, ground's frozen. wait 'till never.)
These are my non-plumbing professional thoughts on drain cleaning. hope they are helpful.