I always thought calling for snap elections in 2005 was a huge miscalculation by Chancellor Gerhard Schröder (SPD) after his party lost the NRW state election.
IIRC, wasn't there a snap election because the Union & FDP could use the Bundesrat to block any legislation that'd already been passed by the SPD/Green majority in the Bundestag? If so, it doesn't really seem like Schröder had much of a choice.
That's true, though the Union had already done that before the NRW state election. That was one of the reasons no minimum wage law was passed in conjuction with the Agenda 2010 reforms and it turned out to be a huge mistake.
As leader of the opposition, Merkel and the CDU used the Bundesrat to block a number of policies, especially those parts of Schröder's reform agenda that were less controversial. So she actually benefited twice since it cost Schröder the chancellorship and later on because as chancellor she was taking the credit for economic benefits that only were made possible by bold reforms passed under the Red-Green government.