If you try to delete a transaction class (or Resource Class, etc) and get an error saying you cannot, chances are that it's being used on resource profile, WIP transactions, or financial plans.
With the enhancement done in financial planning in v13 the schema for financial plans has changed, adding a new table 'odf_multi_valued_lookups'. Today let's use a query to find out which financial plans are currently grouped by transaction classes and a specific transaction class is used in the plan detail
select inv.code PROJ_CODE, pln.code PLAN_CODE
from odf_multi_valued_lookups odf, fin_cost_plan_details dtl, fin_plans pln, inv_investments inv, transclass tc
where odf.object = 'costplan'
and odf.pk_id = pln.id
and pln.id = dtl.plan_id
and pln.object_id = inv.id
and odf.value = 'transaction_class_id'
and dtl.transaction_class_id = tc.id
and tc.transclass = 'LaborTra' -- replace with your transaction class name
group by inv.code, pln.code
As the Technical Refernece guide illustrates here, you can modify this query to find another attribute by changing out the transclass table, the odf_multi_valued_lookups.value value and the column name from fin_cost_plan_details.
Please, feel free to share your queries here for department, role, etc; or share your queries that finds which resources/WIP transactions use a specific transaction class!