"I have seen a lot of discussion lately about the Military Reaction Level settings for planets and a message about the sequence of events when invading. In many cases the messages posted had incorrect information, probably from people who believe the "TW document". Below is the sequence of events that occur when a ship enters a sector and lands on a planet. I have posted this info before but I have revised a few of the steps to provide a little more detail. This should answer most of those questions about what the MRL is and what happens.
 
The question left is what good is a non-zero MRL? I used to size up my competition. If they were not expert players, or at least not experts in invading, and they traveled around in smaller ships (i.e. StarMasters or lower fighter and shield capacity) I would consider a non-zero MRL. The reason is I wanted to destroy their ship in the process so they can not reload. Even though it would cost me more fighters (2:1 odds instead of 3:1) it would also cost them a lot to replace their ship and all it's gadgets. In addition they would likely lose a lot of turns when they end up in an escape pod and need to use their remaining turns to get a new ship and back to safety.
 
These days I am not sure I would do this. All it takes is one expert invader in the game to mess up the plan, and the quality of my competition has significantly increased. In addition with the bugs known these days, in particular the ship overloading bug, it is much harder to size up an opponent predict what is likely to happen. I take the conservative approach. I assume the invader knows what they are doing and when they come in to invade they will have all their assets ready and take steps to keep from being destroyed. When they come in it is very likely they will conquer the planet (the 1639 shields bug not withstanding). I want to make it as costly for them as I can so I set the MRL to zero because I want all my fighters to get the higher odds." (IWM p.47; ¶1-3, 1995)