There's not nearly enough information in your original question to get a complete/specific answer.
Based on the information you've provided, the answer would be: No, they are not "necessary" or “beneficial” for bulking or cutting.
The only time they would be “necessary” is if your carbs were low or depleted.
If you're “bulking” your carbs should never be low.
Beneficial for the purpose of bodybuilding = change of body composition towards more muscle and less fat,
compared to consuming the same amount of carbs but equally distributed.
In response to this one, I'm assuming that you are talking about not having equally distributed carbs throughout a period of days (Low days and High days) as opposed to throughout each day.
As carb loading relates to “bulking”, the only truly beneficial time to load would be post- workout (for the insulin response & glycogen replenishment). But a carb loading “day” wouldn't make much sense since your carbs shouldn't be low in the first place.
If all of your glycogen stores are full and you have a loading day, your body will just store the carbs as fat (assuming you are eating above your maintenance level of calories).
As carb loading relates to “cutting”, it is my opinion that you shouldn't have severe low days and high days unless you've already exhausted every other option.
BTW, I'm basing my response assuming a "Natural" Bodybuilder. A Natural bodybuilder would loose too much muscle doing extreme low days & high days, whereas a "Drug" Bodybuilder could get away with a lot more on the extreme low days due to the anabolic/anit-catabolic effects of the drugs. However, I still don't believe a drug bodybuilder should do the low/high days until they've exhausted every other option.
