A member of our organization was experimenting with tile services recently and uploaded a layer and generated a tile service as an experiment. She was so excited about experimenting with the capabilities that she forgot that she would use credits in doing so. The experiment cost our meager little organization 1,600 credits worth $160! If she had been prompted with a message before proceeding, she would have known to stop. We have had several similar issues in the months since we've been using AGOL for Orgs, though none quite so costly.
This idea has been merged with ArcGIS Online Warning/Estimation Button when using credit costing services.
When a user tries to execute a process that would consume credits in AGOL for Orgs, they should be told that's what they are doing and given an opportunity to stop. So the message might say...
"Generating tile overlay will cost approximately 1,600 credits ($160). Are you sure you want to proceed?"