An RSP is the sole means of reporting in CM. For most admins, installing this role directly on the single primary in their hierarchy will be rather common simply out of simplicity and financial constraints.
Larger companies that have a Central Administrative Site (CAS) are also likely to install the RSP on the CAS for the simple reason that buying more RAM to get by is cheaper than managing another server for reporting.
Should you wish to offload this role to another server, the major requirements are x64 OS and SQL (IIS not needed). Review the CM supported configuration documents at https://technet.microsoft.com/en-us/library/mt589499.aspx for up-to-date information for required OS and SQL versions. The performance will be directly tied to the speed of disk and amount of memory. A simple VM with 2 GB RAM is not a good candidate.
We will start with installing SSRS on the CAS or primary, and then later show what to do if you want SQL on another...