Tires are expensive and I always try to use them for as long as possible. However, tire wear is more than just the tread getting shallower. The casing breaks down and the sealant weaps through the sidewall and the tire flats more easily from both punctures and tears. Knobs get torn off. The bead stretches and sealant weeps and the tire is more likely to burp or come off the rim. The rubber ages and cracks. With every mile you ride and day that passes the tire gets weaker and weaker, so don’t push this to far and end up injured or stranded. Inspect that tire before every ride. If you have very smooth trails you might get away with a lot. If your trails have a lot of sharp rocks and roots, you’re playing with fire.