White balance does not change the underlying RAW sensor data. The camera’s WB setting is typically stored as metadata and used for the embedded preview/JPEG, and RAW software can choose to use that setting as a starting point.

So yes, setting WB in-camera can still be useful when shooting RAW-only, because your converter may read that metadata and apply it initially. But you are not locked into it—you can change WB freely during RAW processing.

If you want the most accurate neutral reference in post, taking an actual photo of a gray card is helpful, because then you can use that frame (or an eyedropper tool on a neutral target) to set WB precisely. If you don’t photograph the gray card, the in-camera custom WB can still provide a good starting point, but you won’t have that reference shot available later.

In mixed or changing lighting, many photographers still shoot a gray card frame for reliability.