From Dr Might's post:
"A subject should be informative, and about 72 characters or less.
If the entire email fits in the subject, put it in the subject.
If you think that's rude, it's not.
If you insist that it's rude, put "Thanks!" in the body.
If the email fits in the subject, it takes a click out of processing it, and raises the probability of a reply.
(If the recipient gets hundreds of emails per day, clicks add up.)
If the email doesn't fit in the subject, the subject should contain the most critical details, such as the date, time and location of a meeting, or the top action item and deadline.
For example, don't send "Save the Date" as a subject.
Send "Event Title, Save the Date: Date."
In short, the subject must provide enough information for the recipient to know how to prioritize and act on an email quickly."
So I'd say the former, it makes the subject more specific.