The most common and most likely answer to this crossword clue is the 6 plus 3 plus 6 letter word SPEAKS FOR ITSELF
I've seen this crossword clue in The Guardian
S
P
E
A
K
S
F
O
R
I
T
S
E
L
F
Buddy explains!
The straight part
We know that "Requires no explanation" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case requires no explanation = speaks for itself.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.