The most common and most likely answer to this crossword clue is the 5 plus 4 plus 6 plus 2 plus 4 letter word WORTH ONES WEIGHT IN GOLD
I've seen this crossword clue in The Times
W
O
R
T
H
O
N
E
S
W
E
I
G
H
T
I
N
G
O
L
D
Buddy explains!
The straight part
We know that "Extremely helpful" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case extremely helpful = worth ones weight in gold.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.