A few people I know hate wargame morale tests of any kind. They say it slows the game down and takes away from the pew-pewing. I can't argue with what someone regards as fun; others like systems with complex morale systems
Morale (in most cases) is usually a test against a morale stat; perhaps if a unit loses xy amount of troops in a single turn, or maybe each casualty if an entire army or unit drops below 50% numbers; perhaps if faced with a terrifying enemy or weapon (flamethrowers ftw).
Other systems (especially in the age of firearms) deal with "suppression" - units accumulate markers, perhaps "pinning" them in place or routing them off the table entirely.
Fleeing troops can often be "rallied" by a successful roll (perhaps by a command or hero unit), or perhaps by breaking line of sight or getting in cover.
But there is pretty good evidence that "willpower" or morale is a finite resource. We have finite mental energy. (This would be as applicable to certain magic or psychic systems). I enjoy the "You are not so Smart" website; so I'll summarise a few interesting points from this article.
Researchers did some experiments to test if willpower was finite: like tell people they were awesome/worthless, then get them to count cookies (yes, as expected the "rejects" gorged themselves, having already suffered a blow to morale they couldn't resist delicious cookies); or putting participants in a room with cookies and radishes; one group was told to only eat radishes, others were told to eat cookies; a third group wasn't shown the food. All three groups were then given an impossible puzzle. Two groups lasted ~20 minutes; the poor radish group lasted only 8 minutes. Resisting the cookies and forcing themselves to eat radishes caused some psychic cost. But it isn't always negative uses of willpower; it can be any choice or complex process; for example finding every "e" in a nonsense sentence is easier than searching this paragraph to find each "e" that is two letters distant from another vowel.... Subjects who had the more difficult initial task or decision tended to give up faster on a subsequent task. Conscious choices or exercises of willpower come at a cost; though it is easy to coast on autopilot (like showering and driving to work), manual "executive decisions" come at a cost. Although what is being depleted may just be glucose...
Anyway, this got me thinking to morale systems where morale or willpower is a resource than can be managed, or depleted. I remember AE:WW2 having a "Drive" value that is gradually eroded (or restored) by various actions. Once the Drive score got to zero, the unit routed.
Morale is arguably a much larger determining factor in battle than... pretty much everything; fights seldom go to the "last man" and most usually end with one side pulling back (or fleeing outright). It's much easier to scare the pants off someone than kill them. I think the overall casualty rate in Iraq was around 2% (albeit massively skewed in favour of the Coalition) and Antietam from the ACW was similar. Saratoga was also about 2%. Overwhelming force seems to be a factor; the more evenly matched the force, the longer the contest; the more casualties; casualties also are much higher if the loser is unable to easily retreat. Agincourt was around 25% casualties; Normandy was about 18%. Yom Kippur was about 1%. I'm sure I'll get some nerd in comments correcting my numbers to the nearest decimal; but point is, there was seldom a fight to the last man. Even in battles where one side was pretty much surrounded and slaughtered (Cannae?, WW1 "boodbaths" marching into MG nests) casualty rates seldom exceeded 40%. In short, forces should be testing for morale well before 50% casualties - probably more like at 2%.
Interestingly, I remember reading only 1 in 3 soldiers ever fired their weapon in combat in WW2; and only 15% actually fired at an enemy; in Vietnam 8 out of 10 did; nonetheless a significant proportion of soldiers in shooting combat are not actually... shooting. Combat ranges are also interesting: in Vietnam, only 30% of those who fired, ever fired at under 100m; only 15% fired at under 50m... perhaps a topic for another post)
Anyway back on topic. So morale and willpower are finite resources; someone under stress or making decisions will struggle to make decisions or use willpower on subsequent occasions - which points to morale being a "resource" that can be steadily eroded. Some systems allow morale to be increased due to actions of leaders, but should morale ever improve beyond the rested, pre-battle level, even if sarge is yelling? So tracking morale/willpower as a resource makes sense, albeit perhaps a bit messy (perhaps a micro d6 next to a unit, for example?).
Secondly, traditional wargaming "break tests" at 50%+, while easy to keep track of, seem nonsense; forces will break and retreat well before that; 50% casaulty rates tend to only occur if a army is unable to retreat (ambushed/surrounded) or if forces are evenly matched and the battle goes for a protracted period.
As usual, I'm not advocating a "best method" or even forcing folk to use morale tests at all (I can sympathize with people who want to "fight to the last man" as I myself dislike rules that stop me activating all my soldiers in a turn - even though it would be quite reasonable to have poorly trained troops paralysed/indecisive compared to better trained troops with more initiative).
I'd just like to shine a spotlight on morale; I feel it is often ignored in favour of cool mechanics and "tacked on" as an afterthought - should it be more central to rules than they usually are? After all, breaking morale and forcing the enemy to flee tends to be how battles are won; killing is just a means to that end. Many rules spend a lot of effort on a new mechanic to resolve shooting, or melee - but ignore perhaps the key aspect of warfare.