In which case I will direct you to the wonderful resource of Douglas Adams who's most famous work was based on the premise of people asking questions that they did not understand, and therefore not being able to understand the answer when it was given.
At best offerings could be encouraged to offer what they define sustainable and community as. For instance, if you were to ask the average Tory sustainable would be if it could reliably deliver a stonking profit for six-months before exploding for someone else to clear up, and community would be a vague notion of something that didn't exist. Alternatively, my own definintion would be that a community is the foundation upon which to build a strong society, and sustainable is where inputs and outputs are sufficiently balanced such as to achieve long term, lifetime enjoyment for the mass majority, renewable for future generations.
Perhaps you should revert to the original question setter to discover what they meant in asking the question, otherwise you could end up arguing against the wrong requirements.
However, should such a sustainable community ever be developed to the definitions I prefer then the economic effect would be positive stabilisation and realistic achievable and repeatable growth, the social effect would be greater security and commonwealth cooperation, and the physical effect would be the achievemement of human scale determined environment.
I suppose a saving grace is at least you are avoiding wikipedia - but may I suggest a visit to a library before they close would assist in developing the answer.