I've got a few large dSYM files on my machine, installed by the Qt Framework. As I understand they are used for debugging, however I don't actually need to debug the library itself. Is it safe to delete these files?
Yes, you can delete these debug symbol files safely. These files provide human readable names for code within the framework or application.
Removing the dSYM files will not affect the framework or associated application's ability to run.
Purpose of a dSYM
Should the calling application or framework crash, the dSYM file is used to provide more readable insight into where the crash occurred in the code.
Apple's Technical Note 2151 shows how dSYM files are used – the same approach applies to iOS and Mac OS X.
dSYM for Developers
Ideally, the developer keeps a copy of the dSYM files and does not distribute these files with their application or frameworks.
When crashes occur, the customer sees a technically obtuse crash report which they can report. The developer can then combine their local dSYM files with the crash report and produce a more readable crash report that should help track down the problem.