I see where Audrey's concern lies about assigning the IT Mgmt spend to a metric other than Cost - and Travis has a good point about where you might encounter a circular reference.
@Audrey Mitch are you planning to report this through the out-of-the-box Applications Reports? or do you have a custom report that is locked to the Applications Object?
If you go with Travis' suggested approach, I would ensure that your total spend formula includes both the Cost metric + the IT Mgmt Metric/Cost Driver.
Ex:
Name of IT Mgmt to Applications Allocation = "(Applications) IT Mgmt Tax"
Total Burdened Cost of Application (YTD)
=Cost YTD + YeartoDate({(Applications) IT Mgmt Tax Cost Driver})
Now I'm wondering if you can reference other allocations as the weight basis for your IT Mgmt - App Allocation line...
We have not used this feature for our model because we typically use existing numeric columns in our data or other table transforms for weighting.