I have checked, yes, before, and have had the ability to write in, after interview. It gives the new prospective employer the semblance, that you've nothing to hide, about your current position, yet, informs them, that you value employment, and that expresses, that an employer being contacted, without something being in the works, could be detrimental.

Reference checks, are time consuming, so to me, it seems that most employers wait, until they are a little more serious, before conducting reference checks.

Hope you find something.