Separator plates have a little raised point in the center so your cake is perfectly aligned and held in place. The weight of the entire cake is displaced on the bottom board, not on each tier so it's much more stable and disaster-proof. You still use cardboards but before you even start, make sure and line up your cardboards with each separator plate to mark a hole in the middle of each cardboard. Then stack and fill your layers as normal, making sure each tier is exactly the same size as the pillars (usually 4").
With your largest tier in place on the serving board, take the next-size tier separator plate and press gently into the top center of the bottom cake to mark where the pillars will go. Then insert the pillars into the separator plate and push into the bottom tier. Slide your next-size cake onto the separator plate, feeling the little raised piece "click" into the hole you previously punched in the cardboard. This prevents it from moving around and there is no need for doweling.
I transported a five-tier cake down the roughest road in the county this summer and it worked like a charm.
Not sure if you've seen this one but it basically explains everything I've just said in greater detail and with photos