I forget the details, but do recall that the installer asked me where to put the temporary files, as well as the sample data. You could re-run the installer just to see where it put them.
I installed Samplitude on my C: drive (SSD) and everything else on my larger E: drive (conventional drive) where all my other samples reside. In any case, there is also an option to delete the install files after installation, so as long as you have room on your C: drive you can just leave the default as-is and you'll be OK if you're concerned about space.