The most common and most likely answer to this crossword clue is the 3 plus 4 plus 6 plus 4 plus 2 plus 2 plus 3 letter word ALL GOOD THINGS COME TO AN END
I've seen this crossword clue in The Guardian
A
L
L
G
O
O
D
T
H
I
N
G
S
C
O
M
E
T
O
A
N
E
N
D
More clues leading to the result ALL GOOD THINGS COME TO AN END
Buddy explains!
The straight part
We know that "Why tapering items are best?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case why tapering items are best? = all good things come to an end.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.