There are benefits and negatives to having multiple henchmen in one group, versus one henchman and multiple groups.
Multiple Henchmen in One Group:
You won't lose the group if one dies. If one gets LGT, the group is still there as well. This is most advantageous for groups with good advances, but that gets aspensive to replace.
One Henchmen per group:
Better chances of Good Upgrades, including LGT.
But if they die or get LGT, the group vanishes and any henchies you hire get base henchies.
-Thrasher Kitch