This is what
Arreat Summit has to say about Freezes Target:
Hit Freezes Target
This bonus is pretty obvious. Items with Hit Freezes Target has a chance to Freeze Targets. Formulae:
The chance of freezing is 50 + (AL + (B*4) - DL) * 5
AL = attacker level
DL = defender level
B = freeze bonus from item (default is 1)
if it's ranged, the AL has a -6 penalty.
if it's ranged, the chance is divided by 3
freeze length = (chance - roll) * 2 + 25 frames
with a minimum length of 25 frames (1 second) and a maximum length of 250 frames (10 seconds)
PS: It's also a useful mod when you want monsters to shatter (like on IK set for example).