A "blocking," or "block cue" contains hard values for every parameter of every fixture and an intensity for every dimmer channel. Express(ion) called this an "AllFade" and would insert hard zeros for every unused channel. Not only does this prevent information from previous cues from tracking through, but also, in a multiple cuelist situation, it prevents other active cues from altering the look you have recorded (depending on the settings of cuelist priorities).
At a minimum, one probably wants the first cue of each act, as well as all fades to black, and all cues immediately following fades to black, to be "blocked" cues.
At a minimum, one probably wants the first cue of each act, as well as all fades to black, and all cues immediately following fades to black, to be "blocked" cues.