When it gets down to that part of the season it often can be. For instance, say North Dakota is the #4 overall team, so the last #1 seed, and let's say they draw Alaska-Anchorage in the 1st Round of the WCHA tournament. If we sweep Anchorage, they drop below .500 and have no remaining games, so will not be a TUC. Now, if we win two out of three, they stay above .500 and will be a TUC. If they are a TUC we get a 4-1-0 record under that category. Our RPI would not take too much of a hit, and an additional 4 wins and only 1 loss to TUCs could flip more comparisons than the difference in RPI would lose comparisons. In that situation, it would be better to win the series in 3 games as opposed to 2.
It obviously depends on the scenario, but winning a series in three games can sometimes be better than sweeping a series. That's a flaw in the system.