The default maximum disk space allocation for some versions of BOINC, and for some WCG device profiles, is set at 4. This may not be enough, as I learned yesterday evening, when I noticed several red lines of message as follows:

Message from server: No work sent
Message from server: No work is available for … (projects selected)
Message from server: The preference you set for maximum disk space used by BOINC has been exceed by xxxx.xx MB

The highest value for xxxx.xx recorded was 1504.31.

I changed the setting: Use at most x.xx Gigabytes disk space to 10.00, which solved the problem.

Here are the details:

Processor: Intel Core i7 980X with 12 concurrent threads.
OS: Windows 7 Home Premium 64-bit

Work units running at the time were a mixture of C4CW and CEP2 Windows beta.

If you have a fast system running several concurrent threads, I recommend increasing your BOINC disk allocation.