Reverbs, simulating the millions of tiny echoes that naturally bounce off the walls in a room, have become an central part in glueing together sounds in a song. There are likely few tracks today that don't contain reverb in any form.
Reverb is a simple but powerful reverb, which helps you to quickly tune in the character you want. It adds the sense of space to any sound by emulating the sound bouncing off the walls in a physical room:
Reverb 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.
Reverb is also available as a Rack Extension for Reason over at the Propellerhead shop.