Changing _x/_y, and "rendering"

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i put the word rendering in quotation marks because, as you’ll soon see, i probably don’t know what the hell i’m talking about… after having browsed these forums for a bit, i’ve seen people say things like “changing _x/_y values mid-code is bad, have your velocity code do that”, and i’ve seen people mention things about the way flash draws objects (or “renders” them… am i using that word right?), and i was just wondering: when you change the _x or _y values for a movieclip, does flash IMEDIATELY execute the code to redraw the screen to reflect those changes, and that’s why it’s better to have all location changes made at one single point along the main game/movie loop? if so, is it good practice to have “soft coordinates” declared for each MC, which can be altered mid-loop, and then have the real coordinates set to the soft coordinates at the end of each loop?