SQL Server's Servicing Rules Have Changed
Microsoft has dramatically changed the support policy for SQL Server. In the past, the policy was essentially "wait for a service pack unless you have a problem". There were cumulative updates (CU) available, but Microsoft strongly discouraged their use with warnings such as:
“This cumulative package is intended to correct only the problems that are described in this article. Apply it only to systems that are experiencing these specific problems.”
“A supported cumulative update package is now available from Microsoft. However, it is intended to correct only the problems that are described in this article.”
The flaw in this thinking is that DBAs and developers often don't know when a problem solved by the CU was affecting their servers. Working under an assumption that any performance degradation or unexpected downtime is caused be a flaw in their own designs, they may wait months for a service pack when the problem is easily solved.
The new recommend from Microsoft is that cumulative updates be installed using the same process that companies install service packs. Microsoft continues,
As of January CU releases, these caution messages have been updated, we now recommend ongoing, proactive installation of CU’s as they become available. You should plan to install a CU with the same level of confidence you plan to install SPs (Service Packs) as they are released. This is because CU’s are certified and tested to the level of SP’s. Also, Microsoft CSS data indicates that a significant percentage of customer issues are often previously addressed in a released CU, but not applied proactively. More so, CU’s contain added value over and above hotfixes. These also may contain supportability, logging, and reliability updates enhancing the overall experience.
To encourage DBAs to proactively install cumulative updates, they will be offered on Windows Downloads and through the Windows Update Catalog just like full service packs. Previously they would be available only through a "hotfix" server that required a special request to access.
Under the new model, only the most recent CU for a given Version/Service Pack combination will be offered.
EXAMPLE: When SQL Server 2014 SP1 ‘CU9’ is released, CU9 will replace ‘CU8’ on the download center as the latest CU for 2014 SP1. Adding to the example, while an individual issue may have been originally addressed in ‘CU8’, CU KBs will always point to the latest CU (on the download center), which will then be CU9. Clicking on the “A fix is available for this issue” link in the CU8 KB would take you to the CU9 (latest) download.