High number of sub-partitioned table - Global vs Local index

Hi,

We have a bunch of huge transaction tables with partition (range on DATE COLUMN) and sub-partition(hash on ID COLUMN). Most of the reads are going through the ID column where we created GLOBAL index. The main partition on DATE column is to split the old records to have low hit on new/latest data. We didn't create any index on DATE column. Now, the question is whether having GLOBAL index on ID column alone is good or bad. What's the recommended approach in this scenario?

Thank you!