I don’t think it matters if you have the same slab in both... and it’s not like you have to have the same cabinet color, or paint colors in each bathroom if you have the same slab; or you could, and that’s fine too.

Typically, the master bath is designed differently than a regular bathroom but there is no reason that you can't do the same slab of granite at both bathrooms. It is up to personal preference.

IMo the master is done to go with the Master bedroom so if the other bathroom has the same color palette go for it.

Just because you have the same stone doesn't mean the walls have to be the same. If you have a black and white stone, you can put a rich cream color in one and you can put pink or blue or purple or gray or lavendar or gray in the other one... :)

I looked at remnant stones for my bathrooms, I found a remnant which was large enough to do my 6’ master vanity, shower curb, niche shelves, and the 2nd baths 48” vanity top. You don’t necessarily need to be looking at full slabs.

The two bathrooms are nothing a like even though they have the same countertop. It is a quiet quartz and I took it in different directions in the different baths.

Theres no rules for this - get what you love - there are other ways to change up the space - paint cabinet colors , towels, tile... If you have to pay for a while slab of material - use it up!