One of my favorite rules in FAB Battle of the Bulge is assets, especially as they relate to artillery support.
This ides has been kicking around for a while. Assets appear in games in the old Victory Games title Korea, as well as in the TSR game Red Storm Rising. Still, the idea seems under used a bit to me.
It works well for artillery and is, I think, more realistic than having artillery units on the battlefield.
For one thing, artillery units are maneuvered on the battlefield in the same way as line units by higher headquarters. Positioning artillery units is a technical, as well as tactical; task, and is generally done as staff work, not command work. In this way it's similar to engineers, logistics and other supporting tasks.
Secondly, whenever artillery units appear as discrete units on a game board you can guarantee they will be misused by the player to hold a part of the line.
Now, it's true that artillery units sometimes find themselves in the front line by accident, and there's a rule covering that eventuality in FAB Bulge, but I'm not aware of cases where artillery battalions were deliberately placed in the line to hold a portion AS artillery. That's not to claim that it never, ever, happened, but it's very very rare and not something that should be available as a routine game tactic. It should only be seen as special rules in historical battles where it did occur.
On occasion, when infantry manpower is in very short supply, an artillery unit may be reorganized into infantry and given a sector. This happened to the 45th AA Brigade in Italy in 1944, when it was reorganized into Task Force 45. The required retraining and re-equipping the unit, and it's notable that it was an AA unit that was selected, not a field artillery unit. Given Allied air superiority the unit was excess to needs, although it's possible German practice in this regard was superior, using AA guns (such as the feared 88) as direct support.
There are a lot of reasons for this, most of which are hard to reflect on a boardgame table.
For one thing, artillery crews are trained technical specialists and very difficult to replace. On occasion an army may have to risk these troops in direct battlefield support roles, for example the World War II Soviets, but most armies are loathe to risk losing these troops even in direct fire support -- so using them as riflemen makes even less sense.
A second factor usually missed by wargame designers is that an artillery battalion can't hold the same amount of ground as an infantry battalion. While a cannon unit has a high firepower value, it has a low manpower value, especially if you're going to man the guns with an adequate crew. Artillery batteries don't have a lot of extra guys to spare to man the perimeter. They're often reasonably well-equipped with machine guns, but they also have a lot of vulnerable targets such as the guns, the ammo and their transport.
Often wargames over estimate the ground-holding ability of artillery units.
Treating them as assets, instead, gets around most of these issues, keeping the guns in their historical supporting role without tempting the player down the road of unhistorical tactics.