SSMS 2014 working with SQL Server 2005 instances
My motto is to always use the most recent version of the tools and always have tools >= highest engine you manage. Generally, most of everything in modern versions is backward compatible going back as early as 2005 instances.

There are a couple of exceptions, in addition to those others have mentioned:


For SQL Server 2000, I always install the 2000 client tools. 
If you use DTS/SSIS you will want to have the tools relevant to the version of your packages. If you open a 2008 package in 2014 and save it, you will cause problems for other users still using older versions. This may also be true for maintenance plans.


The nice thing is that you can install both the 2005 version of the tools as well as the most recent version side-by-side. This way, if you come across any compatibility issues, you can fire up the older version. 

In general, you should be able to use the newer version for just about everything, and not worry about any negative effects on your data (full disclosure though - I don't use the UI functionality for a whole lot, particularly the buggy designers).