The NBA schedules games for teams on back-to-back nights multiple times a season. Although many say this doesn't effect the teams too much, the teams playing two days in a row suffer.
Many times, an outcome of a game is skewed because the team that is playing their first or second game in a back to back has a strong disadvantage. In the 2008-2009 season, twenty two of the thirty NBA teams had worse records in games which were back-to-back (NBC Sports). On average, NBA teams' winning percentage were 9% worse when playing two days in a row.
Scheduling multiple back-to-back games hurts some teams more than others. For example, the Denver Nuggets were 34-10 (.773%) when not playing back-to-back games and only 17-21 (.447%) when they played back-to-back games (NBA.com).
This season, a typical example of this is the Suns vs Lakers this year. In their first two meetings, the Suns got blown out by 19 and 20 points. In their third meeting, the Suns won by a margin of 15 points. The Suns played those first two games after playing a different team the previous night. Not just a coincedince.
Sometimes back-to back games challenge the stamina and depth of teams. However, in the NBA playoffs, where every win matters, the games are never two days in a row. The problem is that teams in the regular season are being tested with back-to-back games, but not in the playoffs. Also, certain teams play a few more back-to-back games than others.