I can't say I've ever noticed this feature before on Dropbox. I came across it while searching for the correct use of the word/term packrat (with or without hyphen). Nice use of the word on Dropbox's part.
Dropbox is yet another NSA whipping boy. Couldn't care less what lame features they're adding.
Dropbox could identify users who are more likely to need to resurrect a file (either because they frequently delete files, or because they frequently resurrect them), and offer them a discount on packrat.
After all, the man most likely to value hurricane insurance is the man whose house was just blown over by one.