The most common and most likely answer to this crossword clue is the 7 letter word FILINGS
I've seen this crossword clue in The Daily Telegraph
F
I
L
I
N
G
S
Buddy explains!
The straight part
We know that "What’s left after smoothing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what’s left after smoothing = filings.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.
What does FILINGS mean?
FILINGS noun- Any particle that has been removed by a file or similar implement; a shaving.
- The act of storing documents in an archive; archiving.
- Something that has been officially filed; a document on file.