Theft is not a big problem on the camino, but there are occasional incidents and it is always best to keep a close eye on any valuables. Pretty much everyone leaves their sleeping bag, backpack, shoes, dirty clothes,etc. behind in the albergue in the evening, but carry their camera, wallet, phone, and other more big-ticket items with them. I usually slept with my valuables at the foot of my sleeping bag, and had my husband watch them while I took showers.
There are occasional reports of boots or other gear being stolen, but that seems to be a rare occurrence.