When it comes to big fish, a baitcasting reel is the only option. Saltwater gamefish are often big and strong, and the conditions in which they live can be very demanding on anglers and their tackle, particularly reels. You can use an inferior reel on small freshwater fish and get away with it, but tough saltwater gamefish will quickly exploit any weaknesses.
Several factors make baitcasting reels more efficient fish-fighting tools.
They often have drag systems that are superior to those of spinning reels, especially since the very design of spinning reels tends to introduce line twist during a long fight. Some tests I ran a few years ago indicated that monofilament line twisted under hard strain soon loses 25 percent of its strength. With baitcasting reels, an angler can also more easily control the drag during a long, difficult fight. While an angler can apply extra drag to a spinning reel by hand-cupping the spool, this requires shifting the cranking hand from the reel handle up to the spool and back again. The baitcaster only has to move a thumb instantly into position on the revolving spool, without any shifting of the hands.