A cob can be smoked a few times a day without much ill effect. A properly caked briar can be smoked a few times a day if you wipe it out, the cake will absorb most of the moisture. A briar with no cake has nothing to absorb the moisture and needs to wiped out if you want to smoke it more than once in a day. The problem with this is that you will never build cake if you're constantly wiping out your pipe. This is of course just my opinion and there will be people with other opinions on the matter. Some people don't like to build cake in their pipes, I am not one of those people, but to each their own.