Not gonna say Im striking the nail right on the head, but it has to do with the lion developing some type of lump or growth in his throat that will cause him not to be able to swallow food of any type therefore starving! Someone else can go deeper into detail, I'm not good with explaining things.
Some people swear by it, others dont.
Me personally, I do feed my lion krill. But I also feed silversides and squid. I switch it up every feeding. I also feed live grass aka ghost shrimp glut loaded with Cyclo-peeze like once a month as a nutritious treat. Also soak all my foods in vitamins for about a hour or so before feeding.