The most common and most likely answer to this crossword clue is the 8 letter word USEFULLY
I've seen this crossword clue in The Daily Telegraph
U
S
E
F
U
L
L
Y
More clues leading to the result USEFULLY
- American lorry emptied after fuel spill in practical way
- Exploit at length for a beneficial purpose
- Part of house full yesterday, conveniently
- EU’s changing positively, in a way that’s convenient
- Sue changed completely, advantageously
- Exploit completely in a beneficial manner
- Effectively consume till the last drop
- Advantageously America caught Laden; top enemy confined fifty years
Buddy explains!

The straight part
We know that "advantageously" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case advantageously = usefully.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 USEFULLY mean?
USEFULLY adverb- In a useful manner; in a way that achieves something