Why is carrier RNA used during the isolation of gDNA from microdissected samples with the QIAamp DNA Micro Kit?

When purifying small amounts of DNA using silica technology, the addition of carrier RNA or DNA enhances the recovery of DNA. Carrier prevents the small amount of target nucleic acid present in the sample from being irretrievably bound. Other typical “precipitation” carriers, such as glycogen, cannot be used. The carrier used must be a nucleic acid, and of a large enough size (>200nt) to bind to the silica membrane.