One of my customers made the observation that it is not possible to uncheck the Data Quality Services component in the Feature Selection screen in SQL Server 2012 setup. The interesting thing was that she clearly recalled that earlier it was possible to select it (the default was unchecked), and we wondered what changed that it now mandated the selection of the DQS installation:
FYI, she was now running SQL Server 2012 with the Product Update enabled using the command line switches /Action=InstallFailoverCluster /UpdateSource=<path to SP1 EXE>. This means the setup support files are those from SP1.
It then came to our attention that in CU1 there was a fix released to ensure DQS compatibility with failover cluster. The issue is documented in KB article 2674817.
Now as per the KB, there is no way to apply the fix (other than a re-install of the FCI ) to an already-installed FCI which had the DQS components previously selected (but which were otherwise not working due to the issue described in the KB.) So to prevent users from running into the same problem if they were ever to use DQS after the FCI installation, the product team decided that post CU1 the selection of DQS is mandatory.
The other angle on this is, what if you are never planning to use DQS, is this selection going to add services, databases or files which are unused? The good news is that the impact is not much; the selection of DQS in the above feature list just drops a DQSInstaller.exe into the SQL BINN folder, which then has to be (optionally) executed to actually complete the DQS server installation. So, if you never run the DQSInstaller.exe, it will not create the DQS databases on the FCI.
To summarize, though the feature cannot be unchecked, in reality it does not add too much to the footprint of the installed FCI. Hope this helps!