The Mute modes decide how effect levels react when a block is bypassed. When contemplating different mute modes it s a good idea to imagine how individual effect blocks would react when bypassed by them. FX Out mutes only the effect s Out level, not the dry sound passing through the block. This is good for effects that add something to the dry signal without disturbing it, like REV, DLY and sometimes PIT, since bypassing it simply removes the added effect. Note that the signal entering the effect will not be muted, so if you recall a bypassed DLY or REV it will send out delay or reverb tails of the sound that entered it while bypassed.
Output turns down the output level of both the effect and dry signal.
PIT it will send out delay or reverb tails of the signal that entered it while bypassed. PIT effect tail will fade out after the effect block is bypassed. This is the mode to use if you want effect spillover when bypassing any of these three effect blocks. Dry signal level will always remain unaffected. Like Output this mute mode will mute all signal in series with it.