I've helped Plaintiffs and Defendants exercise their "strikes" before since I worked for lawyers for over 25 years, and the information helps eliminate/strike potentially biased jurors.
I recall sitting through Voir Dire once on a panel myself.
One Prosecuring attorney asked "Do any of you know the Defense attorney?"
I raised my hand
Mr. ___ would knowing him bias your opinion?
No.
Ok, "Do any of you know ME, the Prosecuring attorney?"
I raised my hand
Mr. ___ would knowing ME bias your opinion?
No.
Ok, "I guess I'll ask .... Do any of you know the JUDGE?
I raised my hand
Mr. ___ would knowing the JUDGE bias your opinion?
No.
Judge speaks:
Ok MR. ___ would you approach the bench along with the counsel for both parties?
I go up there and they each ask where I know each from etc, I explain that I had taken courses from each Atty and the Judge handled a Mock Trial at school once ... they decide I'm not biased and I go sit down...
Prosecuting Atty continues:
Ok Mr. ____ I see you are ___________ religion, would you have any problem giving someone the death penalty?
No, not if they deserved it.
Denense atty asks ... again Mr. ____ I see you are ___________ religion, would you have any problem giving My Client the death penalty?
Answer: Well,
not having heard any evidence yet, ....(pause) ...
if there is evidence LATER to support what I HAVE heard so far, I sure would NOT give the defendant the death penalty, because it sounds like he was defending himself from the other guy who broke into his house at night and was on drugs, even
IF they were historically enemies from birth.. Even
if the Defendant told the guy 2 days earlier that he'd kill him if he ever saw him again.
IF the dead guy came into HIS house, not the Defendant going out to hunt him down then I can't see anything premeditated on the part of the homeowner, in his house at night, that ....
Judge (before I even finished speaking)
MR. ______, YOU ARE EXCUSED, PLEASE LEAVE THE ROOM IMMEDIATELY.
Me: Yes your honor
As I'm leaving, I see both lawyers smiling and approaching the Judges bench, they are all sort of chuckling by the time I reach the door.
Each attorney gets a limited number of "strikes" to eliminate ones they believe will be unfair/biased ... I saved the attorneys the trouble by letting the judge eliminate me "for cause" because BOTH attys would have EACH used up a strike to eliminate me anyway. And I got to go home early so I wouldn't "poison" the panel.
Yes, the attorneys/parties use that info to attempt to get jurors which are most likely to be sympathetic/have things in common with the party they represent by eliminating those who aren't...... Defense wants a jury of "peers" , Prosecutors want the opposite of what the Defendant is.