Explain on examples, for what specific purposes it is necessary to use roles of the server 2008 R2?

Question

Windows Server

In particular, the following roles are of interest:
1) application server
2) AD LDS service
3) file services
..
It is necessary to locate the client server database on the server.
A database server is installed on the server, clients + a program for working with the database are installed on users.
A folder with a database is shared on the server, and users work with this database through the program.
I just don't understand, is there a need to put these roles on the server?
Another server is used for file trash.

Answer 1

The interface for adding server roles has a description of each role.
Read the description carefully. If your application does not use what you read, then you do not need this role.