Hi Josche,
My view would be, this is about consumption of space in the aggregate, so if you thick provision those vols and they consume 96% of the aggregate space, then yes, absolutely you would be impacted potentially by performance issues and the risk associated with an aggregate that full.
However if those same volumes are thin provision and consume 70% of the aggregate, then no, you are not affected by the risks of full aggregate as you are NOT consuming that space, it only becomes an issue when you actually do consume the space, not the potential to consume it.
Hope that helps