There are many ways to incorporate refeeds into a fat loss diet. Instead of arbitrary refeed frequencies (e.g. once per week), I tend to like to set up a diet so that the client is dropping 1 lb. below baseline every 3-7 days (preferably 3-5), at which point I will throw in a refeed on that particular day.
3,500-4,500 kcal refeed days (biasing towards simple high glycemic index carbs) seems to be a good range to shoot for—not too conservative where the refeed just feels like a tease with no benefit on muscle retention, psychological satisfaction, paradoxically facilitating fat loss; and not too excessive where it would take too many days for bodyweight to baseline and also leaving the athlete feeling disgustingly bloated/full/gassy, lethargic (constantly wanting to nap), brain fog, inability to concentrate, unproductive all day, interfering with training, insomnia. Many will find that controlling for kcals, proportionally higher carb refeeds allow them to dip below baseline faster than higher fat refeeds.
At the end of a diet—when an athlete is very lean—I may throw in refeed days every time they dip 0.5 lbs. below baseline (instead of 1 lbs. below baseline).
Refeed days are not necessary if you are in a lean mass gaining phase. In fact, they are probably counterproductive leading to unnecessary fat gain.