I don't actually think it's reasonable to expect the opponent to know your codex -- there should always be some explanation. Ok, it's all fine that my army list says a guy has "Neuro Web System Jammer", but what does that actually mean? What do psykotroke grenades do, and are they different than psyke-out grenades? (they are) What the hell is a plasma siphon? Is an Iron Halo any different than a Rosarius (no, actually).
In practice I skip it with a lot of the more seasoned players I know....not because they know every little thing every piece of wargear does, but because they have a vague idea what the army does and what questions to ask.
But yes, for any newer player or player I don't know, I start saying, "this unit does this, and that unit can do that, and just so you know my hammerheads have sensor spines, etc.".