Not true. In most circumstances it's considered not wise - you get what amounts to another judge in the jury room.
But my dad, who was a courthouse lawyer (civil - both plaintiffs and defendants) for 50 years, served on juries twice. One of our federal judges here got on a state armed robbery trial. And just last year I was called, voir dired, selected, and served. They elected me foreman. We reached a verdict. :-) . And I tried not to be a second judge in the jury room - but the other jurors naturally looked to me because of my perceived expertise. At least I took down the most important jury instructions in shorthand so I wouldn't be relying on my memory of the charge or my personal knowledge of the law . . .
It's traditional for the lawyers to lie in wait for the jurors after they're dismissed . . . so much so that the judge informs the jurors before dismissing them that they don't have to talk to the lawyers if they don't want to. But I was lying in wait for the lawyers . . . asked them, "What were you THINKING?!?!?!?"
What they were thinking is that they had other folks they needed to get rid of worse than they needed to get rid of me, and they ran out of strikes (civil trial). Good call for the side that won, bad call for the side that lost.
But that's exactly why it's important to show up and be counted - even if you don't think they'll take you in a million years. You can't predict who else will be on that panel, and even if they strike you, you took up a strike that they won't have to use on somebody else (like me.)
So my hat's off to Ted Cruz for doing his duty.
Thanks for the info.