In a good opinion from the Court of Appeals today, State v. Gollas-Gomez, the defendant's convictions were reversed because the trial court refused to remove for cause a juror who admitted that he would be partial in the state's favor. Both sides are guaranteed the right to an impartial jury.
The issue was well-preserved, including the fact that the defendant used all of his peremptory challenges, a requirement for appealing a trial court's decision not to remove a juror for cause.
And the juror was ultimately seated on the jury.
Had the juror not been seated on the jury, because the defendant used one of his peremptories on the juror, it is likely, under current case law, the convictions would not have been reversed, because (1) no harm if the biased juror is not seated on the jury and (2) defendant does not have a due process right to peremptory challenges.
This puts defense counsel in an awkward position. If the judge refuses to remove a juror for cause, the defendant can still remove the juror (to avoid poisoning the trial) but gives up the issue for appeal. On the other hand, it's just one juror, and who wouldn't want to good basis for reversal, especially on multiple measure 11 charges, even if the only way to do so is to leave the juror on.
There may be a way around this. The defendant does not have a due process right to peremptory challenges, but if peremptory challenges exist, the defendant has a right to the same number of challenges as the state. There is no reason the state should have an advantage. After all, if a statute or UTCR expressly gave the state more peremptory challenges at the outset than the defendant, that would be a clear constitutional violation. Why should it be any different if the same result is achieved by an erroneous ruling by the court that effectively reduces the number of challenges a defendant has?