If you're an adviser, none whatsoever...

PI cover, despite the cost being passed on to advisers in one way or another, covers the AFSL holder. In the event of a claim against an adviser (for whatever reason), the AFSL provider can choose to claim against it's PI cover, or not to claim against it's PI cover.

They may decide not to claim due to either... the smaller cost of the claim or the expected increase in PI premium upon renewal the following year, or, in fact any other reason they can think of...

In such a situation, it will be the adviser who has to pay, because the AFSL holder is in a position to enforce such a situation.

Ergo... "compulsory" PI cover is not likely to be of value.