A braided shock leader is a thin, very strong leader tied ahead of a fine braided main line. It lets you cast a heavy lead or a full spod a long way without cracking off. It is especially suited to spod, marker and long range work.
The advantage of a braided leader is its small diameter for its strength. A thin leader flows through the rings and the knot is smaller than with heavy mono, adding distance.
It is the natural choice with a braided main line, for example on spod and marker rods. Braid does not stretch, so you keep full contact with the bottom all the way out and feel every stone and weed bed as you draw the marker lead back.
Braid is slippery, so use a knot designed for it and always test the join before casting. Check the fishery rules too, as some waters do not allow braided leaders on fishing rods. Replace the leader as soon as it frays.