At university I spent my life asking this question as I attempted to get through my history degree doing as little work as I could for the maximum possible result. I am fairly sure that this is not the best nor most rewarding way to work.
However, I do wonder whether in Christian work this is a question I should ask myself more. Rather than seeking to do things as well as I can maybe I should consider how badly I can do a thing for the same net gain? You see the temptation for me is to do anything I do as best as I can so that people realise just how clever/gifted I am. However, perhaps it would be a better use of time and better for my pride if I got used to trying to achieve the same things badly.
I don't want this to be an excuse for sloppy work however, let me give you an example. When writing this blog I could write it as I think it and not worry too much about grammar, punctuation, spelling and general articulateness. Alternatively I could work hard to ensure that the writing flows well, the argument sounds good, my use of English makes me sound clever etc. Now it may be that a better use of language or the correct grammar does make some difference to people's understanding of what I am writing however, it is more likely that it won't and so I can do it worse and as such use less time, worry less about how I look but get the same gain.
The same principle could be applied to preaching, youth work or whatever.
Maybe sometimes it'd be good to sometimes ask ourselves how badly can I do a thing to achieve what I want rather than killing ourselves to do it as well as we can so that we can feel better about ourselves and slowly burn ourselves out!