My 10 year old shower has some slight cracking where the tile floor meets the tile walls... would it be better to touch this up with unsanded grout or to use a white silicone caulk. The walls and floor are both white tile, although the floor has smaller tiles with a flat finish. What are the pros and cons of the alternatives?

Remove the grout, let it dry as long as possible, wipe clean with denatured alcohol and then caulk. I would not use pure silicone, but siliconized acrylic caulk.

I will bet the framing or substrate has swelled due to a leak or the wrong method of installation.

Jaz