Resting for brownie batter It's traditional to rest dough for some pastries like cookies and breads. I think it allows more time for delicate enzymatic processes, to yield a better flavor.

I would like to ask if this is also applied to resting brownie batter? 

I use a brownie batter recipe with the following components: unsweetened chocolate (some kind of a Paris award winning choco), butter, salt, vanilla extract, white and brown sugar, eggs, flour, a dash of baking powder, and cocoa powder (sifted).
No, there is no benefit from resting brownies, and there would be a couple of small disadvantages to doing it.

Time will decrease the effect of baking powder since its work begins as soon as you add moisture.

Time will also cause gluten to develop in the flour, which isn't something you want in brownies. Gluten development will cause brownies to be tough instead of fudgy/chewy.

You aren't waiting for yeast to get frisky; you don't need or want gluten development; you're not shaping dough. You can and should just go straight to the oven after mixing the batter.