Does the sampling interval have an affect on accuracy for an OSA?

The sampling interval specifies the minimum and maximum number of samples that the OSA can use to record a complete spectrum. With a smaller number of samples, the OSA is able to complete the spectral sweep in less time (faster sweep speed). The trade-off is the possibility of missing fine spectral detail, so it follows that you may want to consider using a high sampling interval.
 
By default, the OSA automatically calculates the number of samples used for the recording, based on the span and the wavelength resolution setting of the OSA. The OSA will record 5 samples per resolution value of the OSA, so each sample has spectral overlap with multiple neighboring samples.