The most common and most likely answer to this crossword clue is the 11 letter word SIGNIFICANT
I've seen this crossword clue in The Sunday Telegraph
S
I
G
N
I
F
I
C
A
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T
Buddy explains!
The straight part
We know that "That’s worth noting" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case that’s worth noting = significant.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 SIGNIFICANT mean?
SIGNIFICANT noun- That which has significance; a sign; a token; a symbol.
- Signifying something; carrying meaning.
- Having a covert or hidden meaning.
- Having a noticeable or major effect; notable.
- Reasonably large in number or amount.
- Having a low probability of occurring by chance (for example, having high correlation and thus likely to be related).