The nooks and crannies get filled with grout. Depending on what color grout you choose, it can dramatically alter the appearance of the tile.

Those aren't as popular as they once were for that very reason. There are many other types now that are smooth. My tile person tells me they are much more in demand nowadays than the ones with crannies. I found some at the tile store and they are very pretty. Here's a pic of when I was trying to match some tiles to my mother's granite.

All those nooks and crannies are filled with grout and then sealed. I had tumbled stone BS in the kitchen of my previous home and it was smooth and easy to clean. I found that the grout filling all those nooks and crannies gave the stone a much softer look. Definitely want to pay careful attention to the grout color. I love the look.