Int reduces the chance of sleeping. 97 = anti-sleep.
The chance of sleeping occurs on attacking.
As a sinx you're supposed to SB->chance to defense gears, next target->put on offensive gears->SB->repeat.
With this said the chance is like near 0 to happen.
From my tests with one on a zerk lk vs a friend lk, I got like 1 sleep after 5 minutes of hitting him at 190 aspd so no, it isn't that needed but some people think that being secure is better and some others don't mind to use one there because it makes it easier for them to attack snipers and have no problems with their ninja sleeps. Depends a bit on if your server has Sunglasses[1] or not and the competition on the server.