For the back of the woofer, worth doing but not as vital. Very easy if done before attaching baffle- assuming that’s possible, most cabinets don’t have a separate baffle like these do
Far more important though is the biggest radius possible on the 2 long verticals sides, helps edge diffraction significantly and improves the horizontal off axis performance, where it matters most. Side wall first reflection points often being the most important.
Top & bottom can be done too but of less importance. I use 3” diameter roundover cutter, does mean the cabinet needs to be a bit wider than the woofer though. Most manufacturers skip this part since it adds a fair bit of cost and complexity to the build, but is well worth doing