If you have a CRM solution and want to ensure that users installing it have the required runtime version there is an easy way to enforce that. Just set the minimumversion to the build number that you require. You have to manually edit the solution.xml file that is inside the .zip package generated by CRM, there is no UI for it.
<ImportExportXml version="5.0.9668.0" minimumversion="5.0.9665.15" languagecode="1033" generatedBy="OnPremise">
In the example above solution import will fail with an informative message if the target organization is running a build that is older than 5.0.9665.15.
Why would you want to do that? Well, initially there is really no good use case but as updates to CRM 2011 (e.g. update rollups) are released it may be the case that your solution depends on a particular feature(or bug fix) that is only available on a more recent version of CRM. If you don't change the value the default is set to 188.8.131.52.
Happy solution building