Res is a bit complex in that sense. There are essentially three types in Delphi:
- auto generated .res files (for forms etc).
- other res files for which you have source (.rc) and are declared with the RC file in project or source like {$R 'logo.res' 'logo.rc'}
- other res files for which you don't have source.
So category one shouldn't be in SVN (so essentially same as other pregenerated files like .dcu/.o or .ppu). Category two essentially also not, since they can be regenerated.
Finally category 3, that should be kept. In older Delphi these were often files to e.g. enable themes while the Delphi version didn't know that windows version. This is less of a problem with Lazarus.
You can also convert category 2 to 3 to simply including the .res (removing the .rc source), so that you don't have to add e.g. an image to SVN etc)
Note that the .res situation is still in flux as Free Pascal is switching from windres to an own resource compiler, which makes using it easier.