If your files are lossless, there would be no difference in sound. Your DAC would see identical streams of bits in either case.
You will hear conflicting advice on this, there is no difference.
This.
I have a bin of all my CDs in my basement. I haven't sold them because I feel a little funny selling them when I'm keeping a digital copy.
But they'll certainly never be used!
I actually got rid of almost all of my old CD collection long ago (15 years ago, I think, though perhaps longer). Out of probably 500-600 discs, I still have maybe 50 of them, stashed away (currently in the garage with all of my other crap).
My motivation for the purge was moving (and, to a lesser degree, storage). With a major packing and moving operation looming, I went through them all and re-ripped the stuff I cared about to FLAC* (and made sure I had good -V2 rips of the stuff I didn't care about), and then kept only the chosen few. The favorites, and the rare items that would be impossible to replace even if I lost it all and had to start from scratch and re-buy it all. Everything else went.
Still, I agree with Matt. I didn't feel it would be morally right for me to resell the discs, knowing full-well that I would be keeping my pristine digital copies. So I didn't resell them. I
gave them away. First to friends, and then to random people at work and whatnot, I gave them all away. The ones left over that no one wanted, I trashed (this mostly comprised poorly cared-for junk anyway, people like free stuff). That is, of course, really no better from the perspective of the copyright holders, but (1) I'll have the utmost respect and sympathy for them when we go back to reasonable copyright terms, like it was for most of the history of this nation, and (2) at least
I didn't profit from their sale. The people I gave them to would have never bought them all anyway. Maybe a handful would have been "eventually sold", but not the majority (and, frankly, as-likely-as-not the people did end up re-buying them from iTunes 3 or 4 years later when that was possible).
I don't regret it in any way and have never needed them.
But, I do have a serious backup plan. If you do it, you
need a backup
system. If it isn't backed up
twice (once locally and once offsite) then
it does not exist. The end. No exceptions. And doing backups manually is not good enough. You need a system, or your backups will become quickly utterly useless when you need them most.
* EDIT: Actually, upon consideration, I think I used APE, and only later converted most-everything over to FLAC. APE existed quite a bit earlier, and I think FLAC either didn't exist, or wasn't widely supported or stable back when I did this. Thanks again, Matt.