Prepping e-coated panels prior to bodywork and primer

What prep do e-coated panels need prior to bodywork or priming? Do I just scuff them up or sand down to bare metal?

Generally, I prefer to leave the E coat on the inside of the panel alone, and DA (sand w/ orbital sander) the outside surface, and completely remove the E coat that will see welding, perhaps bodywork, then etch prime, prime, block, paint,......if the panel is a trunklid, door or hood, then I remove the E coat finish from both sides, E coat is the poormans "powdercoat", it's merely an economical barrier to prevent tne panel from rusting from the manufacturer,, if it has to be maintained in inventory..........

To add, I have found on one occasion to be surface rust under the e-coat. May or may not have surfaced later - was glad I took it down to the bare steel.