Is there even a point to the Grandmapocalypse? Does it make you tons of cookies?
The Grandmapocalypse causes red cookies ("wrath cookies" as labelled in the source) to spawn instead of golden ones, which have two negative effects (Clot and Ruin), replace Frenzy with Elder Frenzy (x666 for 6/12 seconds) and make cookie chains spawn more often. When the grandmatriarchs are awoken, 33~% chance to spawn red cookies, when they are displeased, 66~% to spawn, and when they are angered, 100% to spawn (you won't get golden cookies anymore)
They are alright to have at low cps/bank, but it becomes far more profitable to spam Elder Pledges instead. The Grandmapocalypse as it stands is simply a byproduct of the Science Research, which is fitting thematically, but not as debilitating as it perhaps can actually be.