If you mean if left untreated that it will lead to arthritis, the general idea is if you lead an active lifestyle especially with sports, then it's quite likely you'll eventually get early onset arthritis without the surgery, especially if bad enough symptoms begin while you're young.

Speaking from experience as someone who's active with obvious symptoms in their 20s, my decision to do it was that even with physio, IMO it will generally only buy you more time before cartilage damage inevitably occurs. Physio definitely works until it just doesn't anymore, whether it is 5 years or 15 years later, as progressively worsening symptoms despite physio is a very common theme from those who end up doing the surgery, including myself. Even if this isn't always the case for everyone, I wouldn't want to take that chance because the consequences and regret would be significant. If you are active, symptoms will most likely progress, at which point it would've been better to just do the surgery in the first place, especially while you're younger with less wear and tear.

If you're not that active, or are willing to compromise with activity modification/restrictions and be diligent with physio indefinitely/likely the rest of your life, then you can probably manage without surgery and without as much risk in terms of accumulating premature cartilage damage. I tried this initially, however eventually realised this wasn't viable for me the rest of my life, along with the worsening symptoms.