Is there any case in which it could be interesting to split one same promo into different ones even if the sales are stable throughout the promo period?

The only reason why you might be interested in breaking one same event into several promotions despite not having substantial differences in sales during the promo period is:

• If the promo period is long (More than 3 weeks)
• If there is not a promo in the past you could use as a guideline (similar promotion)
• If once the promo has started, you realize the coefficient you used was too high or too low compared to the sales that are actually taking place.

As the real coefficient doesn’t get calculated until the promo has finished, if you configure a unique promotion, you won’t be able to react on time to potential mistakes on the coefficient used. However, configuring two or three mini promotions during the same event allows you to react as the coefficient will be recalculated once the first promo has finished and used to calculate the forecast of the second one.