I have a shower that has the same tile on the walls as on the floor. Currently there is the same grout all over. It is a wide grout (about 1/4 inch). The area between the walls and the floor has lost some grout. Would it be advisable to use caulk (even a silicone) in such a wide space? Should I try to re-grout?

Remove all loose material and regrout.

I agree with Harold, my shower is tiled and Caulking was used where the floor and the wall joins to Caulking had problem with it every two months it was turning to black and caulking would come loose, two years ago I removed the caulking and replaced it with grout scenic then no problem, Thanks.

John