I pull it at 1 ppm. But ymmv
When your resin is new it'll attract whatever ions to it in exchange for a hydrogen ion. When your DI gets "full" it could release things that it has a lesser affinity for in exchange for something it has a stronger affinity for.
Ammonia generally has a weaker ionic bond to the DI. So if your source water has a lot of ammonia/chloramines then towards the end of the DI life, it could be releasing the ammonia ion that it trapped initially for calcium or magnesium or whatever that it likes more. In most cases its probably fine. For my use case, since it seems like I'm always perpetually QTing fish. I rather not risk doing waterchanges for QT with a possible 1-2 ppm ammonia. Since my water report shows them using chloramines, I know after my carbon blocks imma have ammonia.