Tiled shower still needing caulking?

I am just about finished with a bathroom shower tiling project. I have tile going all the way up the walls, and an acrylic shower pan.

I was told by a guy at Home Depot that you still have to use caulk in some areas. Is that true? Why? I thought that grout everywhere between the tiles and shower base was sufficient. Is caulking a practice that the tile professionals use even after all the grout is in place?

 

You caulk every inside corner. Where one wall plane meets another, and where all the walls meet the floor. Standard practice. Grout cracks when those surfaces move, expand and contract. Caulking stretches, grout does not.

 

Also caulk along the top of the tile where it meets the ceiling.

See this: Shower issue: drywall & latex paint

 

Here is why you caulk corners,

 

Why would you caulk the bottom of the tile where it meets the shower pan or floor?

If grout is a porous material, and water gets behind the tile, don't you want the water to flow down (behind the tile) and out of the grout at the bottom of the tile and finally into the shower pan?

 

Just looks like his picture is orientated 90 to the left. That is a picture of two wall sections.

Water will seep through the cracks in the corners of the shower which is why you use caulk there. Usually unlikely that water will infiltrate and get behind tile on the flat of a wall. If you don't seal the area where it meets the shower pan, it usually seeps to the front of the shower and destroys the drywall and subfloor. You don't find out it has been leaking until the drywall starts to fall off the the wall in that area. Have done many a repair in that area, some requiring tear out of the floor as well.