That’s easy enough.
Now that frags have bleed integrated into them by default, two frag grenades stacking bleeds can kill infinite numbers of groaners, poxwalkers and scab/dreg shooters/melee/gunners/ragers, and any special other than mutants. Infinite numbers, as many as will fit inside the bleed radius, which is much wider than the blast radius. It’s a reset button on par with the ogryn frag and if double grenade procs you can do it with a single throw.
Secondly if you combine double grenade with the other grenade perks you have potentially far more than just three kraks. You regenerate one krak a minute, which can make a difference in long boss fights, multi-boss fights, and against ogryn patrols. You can also get grenades on elite/special kill, and there’s no shortage of those on high difficulties. If you really want to be a cheesy munchkin you can take the perk that reloads your grenades when you use an ammo crate to throw 3+3+3+3+3*1.2 = 18 krak grenades, plus any you regenerate during the fight, plus any you get from killing elites/specials. 18 kraks is enough to kill two chaos spawns by yourself.
It’s good enough now that I felt it worth taking the perk in my post-patch build, all that being said…
This is exactly the way it should work because if players can choose when to proc the double throw it actually has a skill ceilling instead of just being based on RNG hopes and dreams. Ranger duping grenades with his ult in VT2 allowed for far more strategies because it let you spend it exactly when you wanted to, with no RNG. Or save the free grenade for later if you didn’t want to use it immediately and things like conc pots that boost ult recharge speed also translate into more grenades. This was especially true in chaos waste runs where boons complicate things even more.