Bitcrush can be used to create distorting effects that sound like that of scraping analog radio, or inherently lo-fi sound sources, like old video games:
Bitcrush shines on it's own, but it was primarily created to power up the different "Snapin Hosts" Kilohearts offer. These are bigger effects units that utilize all the available snapins and give you a really fun and creative workflow for combining them in any way you can think of. So have a look at Snap Heap and Multipass right now.
Bitcrush is also available as a Rack Extension for Reason over at the Propellerhead shop.