Make Movie is pre-cooked templates where you can change none, or very little, of the various aspects of the encoding. With Render As you get full flexibility to export exactly the way you want to. Make Movie is for newbies who don't understand video encoding principles or terminology, and Render As is for advanced users who need full flexibility.
However, Render as takes you more quickly to advanced render settings. It's another click to get there through Make movie. And you always use advanced render, right?
Ok, The i=frame thing seems to be accurate based on what I'm being told in the Architect forum.
Advanced Render, ok, clue me in. I can't see any difference between Make movie->Advanced render and Render as (menus).
Looks like SVMS9-B (platinum) doesn't ive me any i-frame options.