Microsoft published a white paper named "SQL Server Seperation of Duties". Security always an important problem for DBAs and many organizations are made sysadmin by default but sysadmin role gives them full control over the data. The basic idea behind Seperation of Duty is to create user for basic DBA jobs not giving sysadmin rights to them. This document is about this concern and worth to read.
You could download the document from the following link.