The play-in tournament might not have killed the playoff "magic number" but it greatly reduced its usefulness.
In previous seasons, a team generally knew about 10 days in advance of the end of the regular season how many games they'd have to win combined with the number of games their closest rivals would have to lose in order to ensure a spot in the postseason, a calculation known throughout sports as the "magic number." But with the introduction of the play-in tournament, the teams that finish the season in seventh or eighth, positions that previously came with guaranteed playoff berths, are no longer assured of a spot in the postseason.