When deleting a category that already contains transactions, all the transactions have their category removed making the calculation inaccurate. Also, any assigned money that the category ever had goes to the “unassigned”.

The ideal scenario would be checking first if the category to be deleted has any transactions and if not, then delete is safe. In case yes, then choose which category to move those transactions to and bulk change them. Also, it should move all the assigned money to the selected category as well.