What does the Applications Developer actually do?
They are able to go under the hood of SharePoint and access most of the parts and pieces of your platform that normally would not be accessed. Ultimately you want to provide a way to make the enduser more productive and give them the ability to collaborate. This often times requires working with the Farm Server Administrators in order to implement solutions on the farm. These folks are crucial to your success and want to make you successful.
Does this require coding?
This role requires some coding experience at some point in time. There are a handful of ways to approarch this, but C# is typically the main staple program of choice if using Visual Studio. Additionally it is helpful to understand the following:
Service based technologies such as ; SOAP, REST & WCF, an other non-Microsoft Web technologies.
Are there layers of SharePoint?
Yes, mostly the SharePoint consumers [end-users] deal directly with the “applications layer“. The Power users operate at the “customization layer” as a result of having a better understand of the product.
Is it necessary to have a developer?
It depends on what your requirements are and how far you want to take a solution or extend your platform. At this level you can determine exactly what can be seen and what services could be accessed.
Which is it, an Applications, Web or SharePoint Developer
It could be one or all depending on your skill sets, requirements, scope of projects, etc. Additionally you want to consider if custom apps need to be developed, which is highly probable in SP2013
What kind of services are you referring to?
An example might be a service called ‘Word Automation Services’. This can be activated in Visual Studio and provides a way for documents to be turned into a .pdf file and then placed in special locations by way of a batch job run at night. The developer would be able to help assess what fields would help trigger this and place the connection for this to happen.
What kind of tools do I need in my developer toolbox?
This again depends on your role and skill level. If your a website developer you are going to want to manage code and client-side solutions.
*In-Browser Tools: Napa & SharePoint Designer
*Web Dev Tools: Visual Studio [Workflows], Dreamweaver or Expression Blend
*Traditional Tools: IDE’s, such as Visual Studio 2012