Right now, alt.binz only displays the amount of free space on the download drive. I would like an option to also display the amount of free space on the target drive(s) where all the downloads will be unrared. For every actively used drive, it would indicate whether the started downloads will actually fit. If it seems likely that there isn't enough space, the displayed numbers (or drive names) would turn red, for instance.
Usually, very large downloads, e.g., DVDs, are only marginally compressed. Therefore, the NZB size is a pretty good indicator for the space requirement of the unrared download.