You can definitely carry information on a CD but the storage space is limited there
. In case of USB drives you can find storage space starts from 512MB to 32GB. If you gift your clients 8GB USB drives then they can carry a lot of documents, spreadsheets, presentations, official information and also unofficial things like music files and movies. You can reuse these drives more than a million times. You cannot reuse the CD so many times for sure. The size is another point and the USB drives are tiny and you can easily carry it in your pocket or inside your wallet.