[ROLCC] Tritone and Full Diminished 

Full diminished chord contains 3 stacking minor 3rd intervals, or, two tritone intervals. Full diminished can resolve to some kind of minor 7th chord very well.
Tritone relationship also leads to a chord substitution possibility for V chord. So a typical 2-5-1 (ii - V7 - I) relationship can be substituted as 2 - 2b7 - 1. It sounds more jazzy when doing it so certain songs or ending can use it.