Imho this is just a bad design mechanic.
GPG just didn't got any ideas how to balance minniion properly.
Because of this problem they just made them to cannon fodder with no gold/xp for kills.
If you take any spiritual ancestor of Demigod (rpgs, rts etc.) one fundamental balancing method is:
Punishment for death of your own units.
Strangely Demigod is the only game with units/summons that I know that has no real punishment for losing your own units.
In every RTS the punishment involves a COST to buy the unit which you totally lose with the death of the unit.
In demigod you just resummon your units.
In every RPG the punishment involves a LOSS OF POWER or HARSH RESUMMON RESTRICTIONS.
In Demigod the mana cost is very low especially coupled with the easy ways to acquire high mana reg (compared to DotA).
The summons have no life timer (unlike to DotA, Guild Wars)
The CD to resummon is very low (compared to WoW Warlock, Hunter or just DotA again ).
I really would like to see any punishment added BUT only coupled with a buff for the strength.
That way they would be more than just cannon fodder which would imrpove the deepness of strategy/tactic of demigod.
The way how Idols and Minions work currently dumbs the strategy involving them down to thinking like this:
Easy question. Because you dont have to think where to command your minions too. It would be shit if they gave exp. That would feed the enemies.
I also think it's a bad idea to give Generals Idol slots while Assassins don't get anything comparable.
Cheap items have a far better gold/effect ratio than more expansive ones. So you are best off with filling every slot first.
Generals got 3 Item slots more and their Assassin builds are also playable which throws especially priests as best HP/sec item out of balance.