Alter Aeon FAQ (Frequently Asked Questions)

FAQ 7.1 - What are the advantages to grouping?

Grouping allows characters to accomplish things they would be unable
to do by themselves, such as killing a large mob for exp or equipment.
Grouping also allows characters to specialize (hitting, tanking,
casting, healing, etc.) in the group making better use of the skills
availible.

You can also gain more experience in groups, especially if you are
the leader.