Fish need a variety of habitat for feeding, resting, protection, and spawning. Largemouth bass and bluegill both enjoy orienting near vertical structure. Logs, trees, brush, root structures, and Christmas trees are all commonly used to enhance structure for bass and bluegill to orient near. This serves to bring predator and prey in healthy interaction, which benefits both populations and your fishery.
Artificial, manufactured fish structures can be employed to serve the same purpose. Benefits to deploying artificial structures include easy deployment and large, three dimensional structure that does not easily catch a hook when fishing. Then there is the consideration for spawning and juvenile fish. Gravel beds in 2-5 feet of depth and complex smaller structure nearby can serve to protect and enhance spawning and juvenile fish survival.