For me it just depends, I've recently de-divisioned some 15mm stuff to make it more generic and less garish, but in the main I do vehicles with all the appropriate formation and tactical signs, ideally based on photos. For games they are just pretty 3D counters, so I sling them together into units as appropriate. If I can use APW Bavarians as standins for Napoleonic Saxons, I'm not too worried about using e.g. 9th SS Panthers as 2nd Panzer Div one's, or 11th AD marked vehicles as generic British.