Dear Patrick,

Why such a question?

In my humble opinion, there are multiple pros and cons for expanding city boundaries. Depending on the stakeholders, each might have different interests between expanding or maintaining (even reducing) the city boundaries.

I would say that the major concern is political and economical as expanding city boundaries for other purposes seem right. Indeed, lots of administrative complications are caused because of ever-expanding cities that end being only one urban area but still divided in multiple cities.

Oscar

One big city is better at managing regional (or metropolitan) problems given its integrated regional governance structure.  But it loses the benefits from competition among multiple small cities in the same metropolitan area, an argument from Tiebout Hopothesis. This is one of the tradeoffs.

One of the problems connected to the expansion of urban areas is the land take phenomena, Soil is considered as a common good, available in a finite quantity. It has a number of function in the main bio-geo-chemichal cycles. The imperviousness of soil due to the expansion of cities is a major problem all around the world.

Urban growth also threats biodiversity, habitat quality and their fragmentation.

Check:

https://www.researchgate.net/publication/7704227_Global_Consequences_of_Land_Use?ev=srch_pub

https://www.researchgate.net/publication/299418324_The_Effects_of_Urban_Policies_on_the_Development_of_Urban_Areas

https://www.researchgate.net/publication/263719552_Using_Spatiotemporal_Analysis_in_Urban_Sprawl_Assessment_and_Prediction

Article Global Consequences of Land Use

Article The Effects of Urban Policies on the Development of Urban Areas

Article Using Spatiotemporal Analysis in Urban Sprawl Assessment and...

Two matters should be clarified in order for a proper — policy reliable — answer be given: the intended meaning of 'expansion' and that of 'boundaries'. SR

As I understand your question, it relates to jurisdictional boundaries and not to the size of the uban area. It is thought by many that larger scale of jurisdictions produces economies of scale. The argument against that is there is a big difference between production and provision of public goods and services. That is, these goods and services can be produced at large scale (think about police training) and yet provided at small city sizes. On the other side of the leger, the larger cities lose intimate control over differences in government produced goods and services (think about differences in parks, for example). The argument against this is that the differences may be slight. Let's say that it is possible to make mistakes in city administration. With large cities, the mistake can be a whopper. With small cities, there is competition associated with these features that can go very wrong (see the comment by Professor Feng above).

I believe that every cities have their optimum size according their various factors. In fact, many metropolitans/megacities (especially in Asia) are struggling to manage uncontrolled urban sprawl which converting irreversible natural resources uses, In another hand, many small towns/cities still need expansion to increase their role/function as a center of service activity for its surroundings and reach economies of scale.

It depends of whose interests will benefit the expansion of city boundaries. In developing countries like the Philippines and from the point of view of local politicians, expansion can mean more IRA or Internal Revenue Allotment from the national government. For corrupt politicians, this would imply more opportunities for kickbacks for more projects. Expansion of boundaries can also mean more elective positions for the political clan and family dynasties. Thanks and cheers!

http://www.springer.com/gp/book/9789811050732

Do you mean a physical expansion or an administrative boundary? For physical expansion, the arguments are the obvious ones (increasing of commuter load, change of land use, ecological degradation etcetera). In terms of administration, there is a trade off between potential increase of efficiency for services due to scale effects, and loosing competitive pressure on local administrations. But this highly depends on the management model applied. 

All cities are expanding we are heading to 80 to 90% of the world population living in cities. The question is not if we will use green areas around cities for new housing. The question is more when the will these grounds become available. The factor of success is  the communication with the he citizens, with the people to gain support for this development. Therefore we need more knowledge on what people in and around cities drives, what are their priorities and when will the support the choices of others, under heat circumstances and how could we deal with these. That will help the global urbanization trend and choices of the people's development of city growth. And this is only the first stage because we not only have to facilitate urbanization we also have to create sustainable cities. That's why my dissertation (2014) focuses  on conditions for sustainable behavior of citizens individually and in group mobilization.