If i select Keep original IDs are there any issues i can expect in the future.
and why schould I check this box? what are there benefits to this setting or should i leave this checked out.
The Keep Original IDs setting requires your M2 to be a fresh instance.
Supposed that you select ‘Keep Original IDs’ in your first migration. After that, you add new data in your M2 instance (after you complete the first migration), then you start the delta phase. In a few cases, there might be an ID conflict issue.
The workaround to fix the above-mentioned conflict is to delete the new items added between the first migration and delta phase in your M2 (NOTE: This conflict occurs only if using ‘Keep Original IDs’ in the first migration).
We hope that helps.