[domelec]

nothing to do with avoiding a brick has playerkp420 has already told u
its to be used when unbricking a console as tristate halts the system bus allowing the nor to be dumped/flashed.

and if u have lost the point on the e3 cable then u can just solder a wire from tristate point to gnd point on ps3
this will do exactly the same thing (puts tristate to 3.3v)
or if u want it to be connected to the e3 then turn e3 upside down with the faceplate facing u, now count the soldered pins nearest u from right to left, find the third 1 in and solder a wire from this point to tristate (this is the sbe point for e3)