Proper Petition Practice Especially Critical in Patent Reexamination
In most cases, the distinction between appealable vs. petitionable issues at the USPTO is quite clear. For example, if you believe that a patent examiner has prematurely entered a final rejection, the appropriate avenue for relief is by way of petition. Indeed, the MPEP states such explicitly. MPEP 706.07(c). Yet, not all examination/reexamination disputes are so clear cut. (See earlier discussion on ex parte SNQ review process here)
The distinction between appealable vs. petitionable disputes is especially critical in post grant proceedings such as patent reexamination. This is because failure to appreciate the distinction between the two could potentially forfeit substantive patent rights.