Not seeing your actual license it’s hard to answer, but in Documentation section there is a doc Dynamics ERP (NAV & GP) Perpetual Licensing Guide Sept 2012 Update which explains the new model, containing further links to more info inside.
Limited can not post anything by design, as they do not have write access to GL (and GL can NOT be among these allowed 3 additional tables).
but all Dimension-related tables do not count against additional allowed, full list of exceptions is in that doc’s appendix.
I would not say Limited is completely useless, bigger companies could use them for bulk doc entry - say, a low-qualified staff (e.g. student working part-time in the evenings [;)] ) simply keys in hundreds of incoming invoices, which later are reviewed / posted by regular AP staff…