Variable Allocations in Dynamics GP allow you to automatically allocate a dollar amount to multiple general ledger accounts based on values in related Distribution Accounts. The allocation percent is based on the values in the distribution accounts at the point a transaction is posted.
The distribution accounts can be normal general ledger accounts or unit account. Using unit accounts allows you to allocate based on non-financial data, like square feet, number of employees, monthly production volumes.
This is the basic screen:
This a quick video that shows it in action: