Read all the entries and realized that all of them are about big blades meant to be carried in the field... My big knives are work specific -they're strictly big butcher knives (Forschner in stainless) meant for cutting big fish. They're kept in my truck and only brought out when needed. Each is a curved blade with rosewood handles - a 10" curved breaking blade gets the most use but its big brother a 12" scimitar is very useful for working fish with larger rib cages (grouper, cobia, dolphin, tuna, etc - in the 10lb and up size range). I've had them for ages and they're kept sharp with a water stone - then lightly oiled and polished dry until needed. Each is wrapped in cloth to facilitate handling (sheaths just aren't appropriate). I first learned to cut fish working as a mate on charterboats down here in south Florida some years ago (and back then we'd cut 100 to 300lbs a day for delivery to restaurants). Having a decent sized and shaped blade makes the work go much quicker any day.
It's been years since cutting great amounts of fish for market was part of my daily routine. These days as a full time guide most of my anglers are "catch and release" types - but every now and then a big fish will be kept for the table and that's when the bigger blades come into play. I've never thought of them as defensive weapons - but they'd certainly get your attention at bad breath ranges...