So if I understand correctly, washing hands does several things–

1. physical exfoliation, which removes some portion of the outer skin layer, along with any bacteria or micro-organisms riding along, 2) by using soap, a base is introduced which temporarily changes the pH of the skin’s natural acidic layer (which is defensive against germs), 3) soap being antibacterial in nature, additional bacteria that remain are killed.

So yeah, good question about how much of an impact frequent hand-washing makes in terms of healthy bacterial biome. I would speculate that in terms of the overall skin layer health, not much. But in terms of ingested germs, especially if one is eating with their hands, such as a sandwich, pizza, etc, I would guess there would be the bigger impact.

source: just a layperson!