Large stacks eat time and cause players to time out, even opponents
A very large stack will eat time from both players' time while it resolves, even from the opponent, and even when said opponent has no possible reaction to it.
Here in the screenshot I attach you can see a large stack of Scute Swarm triggers resolving, from my opponent; at its peak, the stack had over two hundred triggers in it. Each Scute Swarm token entering the battlefield also triggers their Selvala, Heart of the Wilds (correctly, as it happens, because Selvala's trigger only checks the power of the creature on resolution, not on trigger), creating a new trigger. Not only the animation takes time (this stack was running for around 10 minutes), but the process actually counts towards both players' timers, even though I had no actions I could take during resolution (and the interface never prompted me to take any). In the screenshot it is shown how I'm getting a gameplay warning that is completely out of my control, as all I could do was watch the stack resolve — shortly after, when the stack cleared and my opponent ended their turn, the game skipped my turn, as if I had been inactive, never giving me a chance to take any actions at all.
This means that I simply cannot play the game at all if my opponent puts a lot of triggers on the stack — which doesn't seem like it should be a possibility at all, and yet it easily leads itself to exploitation. (I'm not claiming any malice occurred in this particular case; I assume my opponent was playing in good faith. But the fact that it wasn't abused in this instance doesn't mean it cannot be.)