Clean the barrel every time, but the locks about every month or so. That said I have one rifle I do every time. Let me explain. I seal my lock pans to the barrel with a clump of bee's wax, and I don't get fowling, and junk behind the locks. The one I do clean is an 1830 original, and though I seal it, it just seems to get stuff in the internals, thus requiring a full cleaning. Also most of the time we have low humidity most of the time. That little strip of wax does wonders in keeping the lock clean. I also use a molibdium Disulfide grease to lube sparingly, so it doesn't dry out. The outside is cleaned, and lubed thoroughly though. I shoot three to four flints, plus AR's, 1911's, 03's, Garand's, and lots of other guns multiple time weekly, I end up spending probably four to six hours cleaning, so have streamlined my processes, for maximum clean in minimum time.
Bill