NRBH and assuming you are PLACING a DC. If you use all your MF doing any action it negates assault movement.
Another example of this would be declaring aslt move, placing infantry smoke in an adjacent open ground hex and then moving into the smoke. Placing smoke in an adjacent hex cost 2 MF and moving into the smoke hex would cost another 2 MF. Unless there is leader present, giving the move bonus of 2. this would be a non-assault move, despite the fact that you only move one hex.
Also, look at the rule concerning 'minimum moves'. If your opponent is expending 5 MF in a move into a single hex (regardless of what he is doing when he gets there) and has no leader present to lend the extra two MF, then the unit would become CX. Again, NRBH but a unit that becomes CX cannot also be using aslt move.