The ones on the Central Coast definitely marked as a Car Pool park-and-ride - similar signage to train park-and-rides, except a car-pool-ish icon replacing the relevant public transport icon.
They do make sense for the F3 - I'm sure you could have arguments about whether it'd be better to build up the car parks and train services on the Wyong to Woy Woy corridor instead, but given people are going to drive regardless, having these car pool parks (at least in non-Covid times) reduces the likelihood that the F3 becomes a car park itself, which it was gaining a reputation for all too often in the past 10-15 years.