When it hits that point my balls simply land shorter when I take my normal swing. It's opposite of what it would be for other string where lower tension often have the balls sailing. What happens from what I can tell is the the resiliency of the string is depleted and you're left with a rock hard string bed. I wouldn't play with a full bed of dead poly as that is often associated with an eventual case of tennis elbow.
Yonex VCORE 95D - Pacific Classic 16 x MSV Co-Focus 1.18 @ 54/45 lbs