The most common and most likely answer to this crossword clue is the 8 letter word PRODIGAL
I've seen this crossword clue in The Daily Telegraph
P
R
O
D
I
G
A
L
More clues leading to the result PRODIGAL
- Extravagant lord with a pig? That's novel
- Gold pair ordered, being recklessly extravagant
- Lavish glutton entertains staff on a lake
- For mine, aluminium is wastefully extravagant
- Prompt I miss, wasteful
- Lavish spread polar bears love
- Lavish in support of archaeological work most of all
- Wasteful professional, like Vice President Gore
- Extravagant friend, entertaining one, good behind bar
- Supporting two girlsseen to be extravagant
Buddy explains!

The straight part
We know that "wasteful" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case wasteful = prodigal.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 PRODIGAL mean?
PRODIGAL noun- A prodigal person, a spendthrift.
- Wastefully extravagant.
- (often followed by of or with) Yielding profusely, lavish.
- Profuse, lavishly abundant.
- (by allusion to the Biblical parable of the prodigal son) returning after abandoning a person, group, or ideal, especially for selfish reasons; behaving as a prodigal son.