The various Salesforce.com editions offer different levels of functionality, some of which have an influence on the options available for adding custom functionality. For example Group Edition and Profession Edition do not allow custom code extensions to be added .  However Apps from the AppExchange are not bound by these rules, allowing new functionality to be added to even these editions of Salesforce.com .
 

Using Apps from the AppExchange  can save money by delaying or avoiding the need to upgrade to a higher edition.  At the time of writing ,  upgrading from Group Edition to Professional Edition costs $480 per year per user. For larger companies nearing their limits, an upgrade from Enterprise Edition to Unlimited Edition will cost $1,500 per user per year.  This adds up to a lot of money for businesses with more than just a few users.  Clearly, using Apps - many of which are free or at a low cost point - to extend salesforce.com functionality can save a lot of money on license fees.
 

The current shortage of experienced salesforce.com consultants is major impediment to the ‘build-your-own’ approach. With so much demand for their services, consulting companies tend to favour larger deals, giving smaller jobs lower priority and assigning them to lower skilled staff. The level of consulting demand is also pushing up fees, all-in-all creating a cost and risk profile that is unacceptable for small to medium companies.
 

In some cases, consulting assistance may still be required to help deploy an App, but leveraging pre-developed Apps on the AppExchange can certainly limit if not entirely remove the need for external consulting services.
 

At last count there were 1,810 Apps on the AppExchange, most of which are targeting an industry niche or common requirement.  With more Apps being added every week,  the AppExchange should be the first stop for any company wanting to extend its salesforce.com functionality.