I'm not sure if it still applies to prep for prac but you have to attend them, because they take the role and you have to attend at least 80% of the tutes.
Prep for Prac basically...prepares your practice at clinicals, its good to go and get used to the practical side of things.
I don't know what stream you're in, for for diag radiography its pretty helpful, you get to practice projections and ask the tutor questions about positioning/pathology.