Uston called it card eating
It violates Abdul Jalib's True Count Theorim. His title is missleading in that it is not a Theorim in the strict sense, but it proves that the average expectation within the remainder of a pack of partially dealt cards is the same as that predicted by the true count just before that remainder is dealt. The expectation of the remainder is not changed overall.
The hedging effects of playing more than one hand do not change the expectation, it merely lowers the variance of your results. A minus deck is still a minus deck. Trimming the variance in a plus deck is the same as raising the advantage generally, but the same is not true for a minus deck. A player in a minus situation wants variance actually. That player wants to get lucky and get. In a plus deck cutting the variance has the same effect on your bankroll as more edge. In a minus deck cutting the variance is the same effect as raising the minus edge.
What you give-up in card eating is the ability to detect when the cards in that remainder might be ordered such that the cards removed now swing the edge in your favor. You get the same cards coming to you, with less rounds and less opportunity to change your bets.
Simulations of card eating did not properly weigh the amount bet per round, and the amount bet per spot. That was the case until the massive work done in BJA II on the optimal departure point. Then the same math that says you might want to jump out of a slight advantage to find a new shoe, clearly also shows that consuming cards in a minus shoe to get a new shoe is not a good as leaving to find a new shoe.
There is still potential in pitch games to force early shuffles where some variation in the rule of 6 applies. But that is different than playing multiple hands in that the multiple hands force the shuffle and are not actually played. In pitch games the extra hands are actually a bluff. Such a bluff is not the same as actually playing through numbers of hands and cards and should not be thought of as the same idea.
I hope this helps!