Probably one of the most ill advised things you can do whilst reffing a game, anyone commits a 2nd yellow (or indeed a straight red) offence, stop the game and dismiss the player. Extreme yes, but by not doing so you are running a risk of the attacking move breaking down and the " to be sanctioned" player scoring a goal. What on earth do you do then? Allow the goal then send off the scorer who should not have been on the park?!!
Allow the would be sanctioned player to commit another serious foul play tackle when he should indeed be off the park? I have only ever seen or heard of one incident where play was allowed to continue following a foul by a player on a yellow card whose future offence was worthy of a second yellow and a goal was scored and the offender was duly sent packing.
I have however been present at an SPL match where a player on a yellow committed a clear yellow card offence on the half way line, the referee missed the challenge but the assistant thought the referee had seen it but was somehow playing advantage, the move broke down, the assistant then flagged, but only after the player had hit the post with an effort on goal. The question was then asked at high levels, what would have happened had this player scored? The word back from very very high levels was, disaster, a replay.