The Figure 8 Bend aka Flemish Bend is a knot that joins two lines together. For important loads the Figure 8 Bend should be avoided unless the ropes are of the same size and the tag ends should be longer just in case there is some slippage or a stopper knot added.
It is important to note to be certain the knot will hold the two outermost turns moved in snug against the ropes they enclose.
The biggest advantage of Figure 8 Bend is that after being put under a heavy load it remains relatively easy to untie.