Apex is a proprietary language that can only be compiled and executed by the Salesforce1 Platform. The Salesforce1 Platform is not open source and only runs on servers owned by the salesforce.com company. For these reasons, the purpose of Apex is to extend the Salesforce1 Platform beyond its native features. This might be the most important lesson in this book and can be summarized by two simple rules:
Leverage built-in features: Don't waste your time writing Apex code to do things that the Salesforce1 Platform can already natively do. Built in to the platform are robust features for authentication, reporting, workflow, and more. A good Apex developer is familiar with these features and works with them. Not only will this simplify your development process but also enable system administrators to manage items that frequently change. It will also ensure your projects are future compatible with the long list of feature enhancements salesforce.com delivers with each release.
Calculate your ROI upfront: the Salesforce1 Platform uses a per user subscription model. Before you start developing, determine the costs and benefits of the project. When enhancing an existing application, you should always look for some type of commonality between your existing application and your new one, either in data, users, or administration. A commonality of data might facilitate greater accuracy and better reporting. A commonality of users will reduce costs and improve adoption. A commonality in administration will also reduce costs and hopefully development time. If this is your first use of the Salesforce1 Platform or there are no overlaps, then evaluate the development time, which tends to be much lesser on the Salesforce1 Platform.
These might seem like trivial points, but in our experience working on over 500 projects on the Salesforce1 Platform, the long-term success of any project relies on them.