To answer your question, I ordered with just the SSD, no HDD. My reasoning is:
256GB is enough for me (I'm a software engineer, my output is mainly text files containing code)
More heat & noise from an HDD that would get underused
If I have loads of data to backup/store, I could just use an external backup drive, so it's only in use making heat & noise when I need it, not all the time, see above