Well, even though you can't split the vote in the FPTP sense you can sort of shoot yourself in the foot if people's voting intentions aren't what you expect.

Let's say on first preferences there's Lab 38% Lib 35% and Grn 27%. Now, let's say you voted 1 Green, 2 Labor, 3 Liberal, but a majority of the Greens voters in your electorate went for the Liberals in the 2nd spot. The Liberals would then win the seat and you'd have been better off voting for Labor.

Now, that scenario is a bit unlikely in most electorates, but if you take a look at the inner east in Melbourne for example it's not exactly out of the realm of possibility given the Turnbullesque demographic over there.