The RAIM check is needed depending on your navigation. For horizontal and vertical, you need 4 sats. To have error checking, you need 5, You need 6 for it to error trap and null one out.
For navigation such as RNP-AR, the system will use the RAIM check to feed the HIL...(and the HAL alarm limit)
With RNP AR operations, you have to use the RAIM predictor prior to DEP....If the predictor shows insufficient coverage, you cannot use that procedure.