It all depends in what diet you're on. If you are doing a keto diet some might see the carb up day/-s as a cheat day. When your on a "regular" cutting diet, like moderate to low carbs, high protein and low-mod. fat, I think a cheat day is necessary. Why?
Well, your metabolism decreases by time on a low calorie diet, for some faster and for some slower. I think everyone should have a cheat day just to increase your metabolism, bump it up. It also depends on your % bodyfat. If you are +20% of bodyfat a cheatday would be needed every 3-4:th week. From around 15+ you shpould take one every second to every third week. When you get down to 10-12% the hole cutting thing starts to slow and you should have one cheat day every second week. Under 10%, I believe you should have one cheat day every week. This cheat day should stand for OFF day conserning all training what so ever. This day is the day you should take a break from everything that has with cutting to do. It maybe sounds easy, but I promise it isn't. If you already are at 7% bodyfat and would like to reach 5% or so, I promise you it will take more that you think to have one cheating day. It's all about diciplin. This cheating day will increase your metabolism more than you think. One cheat day wont make you gain 2lb of fat or anything, just as long as you don't cheat on any other day than this cheat day, lets say every sunday. So sunday is your Cheat day.
Your mind: A cheat day is more than just good for increasing your metabolism. It's also good in the way It will make you not cheat during the week. This day is your goal to reach, a day you are looking forward to. Therefor it should be easier for you to hold your diet monday to saturday, you have a goal to reach, and that goal is not to cheat until sunday. If you don't cheat for weeks and weeks you might begin to cheat every now and then.
I always cheat once a week when I'm cutting. It allows me to keep my metabolism high during the week and for me to have a goal every week. My goal is to drop 2lb every week. I weight myself on saturday morning, before I start ceating. On the sunday I've gained lots of wather and my bodyweight sometimes reach +8lb in one day, and of course it's not fat. Think of it this way. How many calories would one need to eat to gain 8lb in one day. One gram of protein is 4cals, 1g of carbs is 4cals and one gram of fat is 9cals, you count. Then, how many of these cals would then be stored as fat..?
Anyway, on the monday I've still water left from this cheat day. When you reach the tuesday you should see some nice results, you are harder than you were last wednsday. When you reach friday you have droped more fat than you should had done without the cheat day.
Good luck
BTW: Sorry for the spelling..hehe