The first couple of times we played, covering fire bogged the game down. On re-reading, it strikes me as important to follow the move-fire rules carefully: a figure gets to move and fire, then the next figure in that unit gets to move and fire.

If you shortcut this and use mass movement, just out of habit, covering fire gets very powerful and kinda boring. If you focus on move-fire a figure at a time, while covering fire is always triggered for an entire covering unit at once, then the covering player has to choose his moment; trading certainty for the opportunity to target more troopers at better range. So if a unit is covering, and an enemy unit begins fire orders with attack pattern move-fire from out of cover, then the covering player has to choose how many licks he's willing to take for a better shot at more of the move-fire unit.