USB-Battery load sharing circuit comparison
The nRF52 uses a more efficient system for running off of battery, since the transistor will have almost no voltage/power drop, where as the diode on the 32u4 will always drop 0.25V.

While this does not matter for power efficiency since your linear regulator will waste the power regardless, it does allow the nRF52 to operate at a lower battery voltage, since there is not an additional 0.25v drop infront of the regulator.

In summary (Rough Numbers due to load dependent):
The 32u4 will stop regulating at a Vbat ~ 3.65
The nRF52 will stop regulating at a Vbat ~ 3.4

All things the same, the nRF52 board will be able to fully drain the last ~10% out of a Lipo battery, while keeping a well regulated 3.3V line the whole time.