Besides missing some of the benefits of Event Sourcing, are there any other drawbacks to adapting an existing architecture to CQRS without the Event Sourcing piece?

I'm working on large application and the developers should be able to handle separating the existing architecture into Commands and Queries over the next few months, but asking them to also add in the Event Sourcing at this stage would be a HUGE problem from a resourcing perspective. Am I committing sacrilege by not including Event Sourcing?