What is the impact of a peremptory challenge on a jury?

[22 Cal.3d 289] In my opinion, any analysis of the issue should begin, not end, with a consideration of the single most persuasive, if not controlling, case on the point, namely, Swain v. Alabama (1964) 380 U.S. 202, 85 S.Ct. 824, 13 L.Ed.2d 759. In Swain the United States Supreme Court dealt squarely with the use of peremptory challenges to eliminate black jurors from a petit jury which was to try a black defendant. In its affirmance of the underlying conviction the high court stressed the importance of the use of the peremptory challenge in impanelling impartial jurors while describing the practical considerations which affect its exercise.