Two settings on the Model Sampling Flux node that, despite the naming, are NOT the resolution of the output/latent image — they instead affect how the model renders internally (exact mechanism unconfirmed even by the demonstrating source). They interact with Max Shift/Base Shift: raising this value narrows the usable Max/Base Shift range before outputs degrade.
1024x1024 is called out as a good default — it gives the widest practical range for playing with Max/Base Shift.
Leave at 1024x1024 as a default for the widest Max/Base Shift range; only raise it (768, 1600, 2048...) when deliberately narrowing that range or exploring how it changes fine detail, and expect to need a tighter Max/Base Shift sweep at higher values.