It is used for dealing with two things. Firstly dealing with packages not yet uploaded to Debian (?ProspectivePackages). If you wish to have a package included in the distribution then you file a bug against this package.
The second thing is for noting that a maintainer wishes for help with a package. This is either in the form of an RFH (Request For Help), or in orphaning a package, or requesting its adoption. The first is where the maintainer wishes to continue working on the package, but doesn't have enough time. The second two are where the maintainer doesn't want to maintain the package anymore. These are a great way for new maintianers to get involved with packaging. This is all organised by manipulating bugs against the wnpp pseudo-package.
See http://www.debian.org/devel/wnpp/ for more information.