Haha very broad question that is really based on the individual, but I'll try.
Essentially if your following PB your going to be building muscle (great!) and eating a diet primairly based on whole foods containing fat/protein (great!).
Now that is going to leave your muscles and liver storage pretty open, as most of the incidental carbs you do consume will be used for daily processing and the workouts (your doing those right?). Yeah there is gluconeogenesis and the krebs cycle but your storage for glucose will still be relatively empty.
So when you occasionally eat carbs, assuming your insulin sensitivity is in order, the carbs should be shuttled to your muscles versus fat cells. That's what SHOULD happen, but that process is highly individualized. On top of that, I wouldn't binge, that could be asking for a dark dark road to a disorder.
Not really sure what you mean by "partly primal". But if were talking specifically diet that is highly individualized also, and generally follows the same guidelines as above.
The 80/20 rule is present in many health books and programs for a reason, because it works. So if you want to *have* (not binge) on carbs then right on!