I found this recent New York Times piece on reading comprehension and retention to be informative and thought-provoking.
Although the author, psychologist Daniel T. Willingham, specifically discusses prose, the concept applies equally to cartoons.
Cartoons often have factual (or logical) gaps that the reader must fill in—but not too quickly. That gap in a well-crafted cartoon might at first seem nonsensical, and when the reader discovers the missing connection (or explanation), the resolved tension produces a laugh. If that resolution comes too easily, or is overtly explained, the gag is unsatisfying.
In his contribution to the blog 10 Rules for Drawing Comics, Zippy cartoonist Bill Griffith concisely says, "Ambiguity is OK. Ask the reader to meet you halfway."
Another example that speaks to me as an artist comes from saxophonist Steve Lacy's transcription of notes from pianist and composer Thelonious Monk:
Don't play everything (or every time); let some things go by. Some music just imagined. What you don't play can be more important than what you do play.
Monk's advice can be interpreted as encouragement to edit, but it also applies to that idea of the audience filling in the gaps.
Of course, I spend a lot of time thinking about the structure of cartoons, so maybe my mind is simply using my own interest/obsession as a way of connecting the observations of Monk and Willingham to Griffy.
In any case, the Times article is well worth reading (and comprehending).