There are three levels of return on investment (ROI) of IC campaigns: gold, silver and bronze.
To put this into perspective, let's say you were launching a healthcare cashback scheme. You know, where employees can claim money back for dentists, opticians, massages etc. Your organisation will have paid for the scheme and would expect at the very least for employees to claim more money back than the organisation has spent.
Granted, it's not always easy to link comms campaigns to money (gold), but almost everything can be linked to behaviour change (silver). Engagement (bronze) can be used as evidence of comms involvement in achieving high gold and silver results; but on its own is unlikely to impress senior leaders.