how so?
Here are a few reasons, but I'm sure there are others. CD's don't have to be ripped in real time - allowing multiple passes to ensure the data is correct. A transport has to do it in real time and depends on the condition or quality of the media - there is more likely to be errors.
Another advantage is that on a music server the files can be buffered into memory, not having to rely on a mechanical interface and avoiding any data bottlenecks.
Compression isn't really the issue, it is whether it is lossless or not. Performance in decoding lossless compressed files does require more processing, so it may sound worse on some systems, but I would guess that it is system dependent and less of an issue as computers improve.
A final advantage is the convenience, a music server makes the process of listening to music very easy. Music is much easier to find and much quicker to start playing. The same CD can be listened to in many rooms without having to physically retrieve it. Also the CD becomes an archive - not being used, so that it remains in pristine condition if you should ever have to re-rip it.
Jim C