Personally, I spend zero time training lower back, or programming it for clients. In 20 years, I have yet to meet a client who needed additional low back strength. People tend to have limited hip and thoracic spine mobility, leaving the low back muscles to translate force between the hips and torso, generally causing strain or worse.
I spend a great deal of time working on mobilizing those joints that are supposed to be mobile – ankles, hips, t-spine, shoulders – and working on the muscles that stabilize the joints that are designed to be stable – knees, lumbar spine, scapulae.
Since the low back muscles typically handle more load that they are meant to, they are tighter than the ideal, and in a state of constant extension. My clients spend lots of time performing anti-extension exercises, variations of planks, etc., to begin to bring their lumbar posture back toward neutral.
Hope that’s helpful!