The reason why sealing the stones helps is that it closes up the pores of the stone, so grout can't really get a hold on the stone. With porcelain, it has virtually no absorbsion, so this isn't an issue.

I have ceramic tile with a stone accent strip (and the pebbles).

I sealed the stone and pebbles prior to grouting to help with grout release. I sealed stone again after grouting for simple sealing purposes, and the pebbles were enhanced/sealed.

If you put sealer on porcelain, you may end up with a hazy film, not desirable. The properties of porcelain and most ceramic tile (exception may be some crackle glazes) make them unnecessary to seal, both before and after grouting.

I too had a textured faux slate porcelain tile floor, that required no sealing, and yes, the texture made the clean-up of the grout a little more tedious, but there really was no grout that adhered to the tile.

For your trim that has stone, I would seal prior to grouting if you are DIY, but just make sure you wipe off all the excess from in the time recommended on the product. If some dries on the surface and doesn't wipe off, you can just use more sealer to "un-dry" it, and wipe well.

Our stone trim border has an irregular surface and we had to be meticulous about getting the grout out of those places (although we did miss some places).