I tried to delete 'Other' subcategories, but MLS would not let me. The subcategories have balances of 0, but still MLS does not allow them to be deleted.
In other words, you verify that the current balance in the subcategory is zero and then you uncheck the "active" box for that subcategory. The subcategory should no longer appear on reports but it won't entirely disappear until the data retention period is over. (In the U.S., this could be as long as 4 years.) This will allow you to look up old information about that subcategory until the retention period is over.