I’ve used it in the past in non-Post Process materials to have an emissive material that adjusts with the auto-exposure. Super useful for gameplay FX that should be visible at all times. But yeah, it’s not working for me in a Post-Process Material and I haven’t looked into it too much.
Exposure is usually done before tonemapping, so it’s possible when replacing the tonemapper that it’s not available? I haven’t tried it in a “Before Tonemapping” material yet, but that could be a start to know for sure. Or maybe it’s just not available in the Post-Process shader.