Brother Captain Peito Akira, 2nd Company Commander, Angels Inferno
Lets Take a look at the Combat Tactics rue for 5th Edition SM's, well Combat Tactics is an ability that enables units to automatically fail morale tests and retreat. Although the idea of turning around and fleeing sounds not very brave or tactical at all, do not understimate this ability. It makes your Astartes, very, very ninja.
There have been several occasions where the rightful application of this rule has saved the SM players men from being assaulted and surely annihilated by units that are close combat oriented. After being shot down by in the shooting phase, my men had the opportunity to either stay and get assaulted or run away using combat tactics. I chose the second option which left my opponent unable to charge that turn and open for a counter-attack the following turn. The only downside is that this ability can only be used when taking a morale check instead of whenever the player wishes to use it so you are forced to take casualties before applying the rule. However, with combat squads, the fact of taking enough casualties to retreat is almost inevitable since it takes only 2 dead to invoke the rule.