Maybe at the whim of utility or AHJ?
I don't find anything about requirements in manual for current model Sunny Boys, just "If there is a neutral conductor, connect the neutral conductor to the terminal block in accordance with the labeling."
From the old SB 5000US manual,
"Automatic Grid Voltage Detection
The Sunny Boy automatically detects the grid voltage that it must feed in. Depending on the voltage
and the phase angle between L1‑N and L2‑N, the inverter determines whether it is connected to a
208 V, 240 V, or 277 V grid. If the Sunny Boy is configured for the wrong grid voltage (for example,
the inverter was configured for 240 V and then connected to a 208 V grid), the Sunny Boy displays
an error message.
...
If the power distribution grid uses a neutral conductor, the responsible authority can demand that a
neutral conductor be connected to the inverter."
With neutral connected and jumpers set for auto-detect, it recognizes which grid configuration.
Without neutral, jumpers must be set for the particular configuration.
This could be useful to me if I put SB on load panel and fed it either 120/240V from grid or two legs of 120/208Y from a 3-phase inverter.