i thought this also. it's a pretty snug fit on my new installation, so my contractor really didn't think it was necessary. he indulged me by doing it anyway on the bath fixtures. but with the matching grout from the tile underneath.

Unless it is a steam shower, I don't think you need to worry about the shower pipe, it is above the flow of water. With regard to the escutcheon, the plate around the handle, often there is a gasket that will seal it behind the plate; if not, you can caulk around the outer rim where it meets the tile.

it was recommended to me (and I have old vintage 1940 fixtures) that as I have escutcheons on shower handles, to take the escutcheon off, and put a "frown" or "rainbow" (basically a semicircle) of caulk above the pipe coming out of the tile, but within the circle of the escutcheon (so that it's hidden), and let that line of caulk dry, and replace the escutcheon. Reason is, water that gets behind the escutcheon will hit the dried semicircle of caulk adhered to the tile, and will roll off the sides, and won't get into the hole in the tile. When it rolls off, it will drip out the bottom of the escutcheon. What you don't want is a full seal around the whole bottom of the escutcheon, as this can lead to trapped water in the escutcheon if the caulk fails on the top or sides. Many of these escutcheons deliberately have a drip hole to let water out.