Go and look how many vitamins and nutrients are lost making white grains and how much the glycemic index rises.

It matters a lot, especially if it's a main part of your diet.

Everything is relative. But imo it’s VERY unlikely to matter “a lot”. Everything is trickier if you’re trying to lose weight, but white rice vs brown is a tiny offender relative to the more common culprits

Why are you talking about losing weight?

That is a common context for consideration of nutrition.