Table field groups and reusability
Field groups on tables are a great way of arranging groups of related fields to be displayed.
The number one reason being that you set these at table level and not form level, so that you can keep this logic separate from the user interface.
When field groups are modified Ax will automatically update all reports and forms that reference them – which is really cool!
Another thing that not a lot of people know is that you can include display and edit methods in your field groups:
Related links (from msdn):