In my case... Depends kung sino and saan ginagamit yung car...

Kung ako lang/City driving, I don't mind kahit ubos na yung thread
Wife and Daughter's car - once the thread hits the markers, it's time for a replacement

Out of town trips and car ko ang gagamitin, then I try to replace a month early (baka kasi may defect tire ko)

***
I know someone from Melbourne (I have a lot of stories from this guy since wais sya sa buhay... better term is magulang)

He bought a tire from a reputable service centre with warranty... Before the warranty ends, I-run flat nya konti yung tire para mag karoon ng side wall damage...

Tire gets replaced and the new tire will have a warranty again, same procedure later...