Did you get an answer?
I am asking the same question.
In the protocols I have found, it has been used as a prehybridization step, along with formamide.
The molecule is pretty big, I suspect it is used to sandwich itself between the two strands of a DNA or RNA, while the formamide deionizes the the bases, stabilizing dehybridization, prior to Probe-hybridization, but I am guessing.
I look forward to hear your thoughts on the matter.