Designing Kitchens and Bathrooms - to grout or not to grout

I am redoing our kitchen counter top and have found some great 12"x24" porcelain tiles. The lady at the tile store said a minimum of 1/16" between tiles for grout. What I would like to know is, why do you need to leave a space for grout? What I was thinking was to lay down my thinset and then put a small bead of silicone (clear) to the edge of the tile and push it against the next tile. Use a razor blade once dried to have a perfect seal between the tiles. Is there something I'm missing about why this can't be done?

Nice theory, does not work. Tiles and the underlayment are constantly expanding/contracting with different conditions. Silicone is not a very good sealer for tile joints, often poor adhesion. No matter how tight the joint appears, it is not tight enough to stop water. Grout bonds with the tile and with itself to make a waterproof joint( if properly maintained).

Grout is basically a form of cement.Just like with bricks,the grout acts as a solid material similar in substance to the tile that locks everything together into one solid mass.Anything flexible,even with a nonflex material behind it,would not do the same thing.Since it's a countertop it would probably be a good idea to use grout sealer to block the grout from allowing water and food residues from soaking into the grout and help control any possible mold or discoloration.Grout is fairly resistant but not 100% and with food prep and wet dishes etc you should probably seal it.

Too add,

If these tiles are not rectified, you would never be able to get a butt joint. Each tile could be slightly a different size. You will even have a hard time getting 1/16" to look even.

Place a few of those tiles on a flat surface as tight together as possible. Spill some water on them, and see if it doesnt make its way into the joints, you have your answer. Now picture the water being something else like milk, juice etc.:)