a quiet place to think about music
James Brown was well known for turning up at recording sessions without having written any songs. He'd just have the idea in his head and when he came in he'd improvise right then and there.
He could also play the drums and the keyboard instruments, so he understood exactly what he wanted. He'd build a pattern with the musicians around the bass and drums, and then bring the guitar in.
All the musicians worked with James for a long time, so they knew what he wanted, and once he got the rhythm section going he would start working with the horns.