Here is where the feature could be helpful...
I have a Z10 that I use for work and personal reasons, with the work use on BES via a "workspace" that is under a very detailed set of policies for security reasons.
I get literally hundreds of work-related emails daily, and many of them include data in them or in attachments that I do not need to keep on my mobile device, but DO need to keep on the laptop on which I work.
The ability to "delete on handset" would help me keep from overloading the storage on my mobile, while still keeping that reference data on Outlook on the laptop - BTW... this data is already subject to a retention policy, but there is a lot of information I may need to access on the laptop but NOT on the mobile - at least after I have seen it and am aware of the information contained in it. For example, I routinely get email with multi-megabyte pdf files attached that I must keep on the laptop, but certainly do not need to keep on the mobile.
THIS is the reason I would like to be able to "delete on mobile" and NOT have it be deleted on the email server.
If this is re-enabled in 10.2, that will be another reason I can't wait for VZW to get it out to us !