I've spent some time on this, so I'll share what I've found... for what it's worth.
Why clean a CD (SACD, DVD, etc.)? New CDs have a mold release compound on them, much like LPs. They may also be covered with 'micro-dust' from the plant where they were pressed. Both impede the laser and cause more error correction. In most cases, you only need to clean (or treat) new discs.
Warm water & mild hand-soap will do about 90% of the job, but a good treatment will do even more (for better or worse - read on...).
I've tried a number of CD treatments, Ultrabit, Liquid Resolution, Shine-Ola and maybe a few more. All provided 'cleaner' sound, but also added brightness to the sonic balance. Liquid Res. was the most neutral of those above (but no longer available). HOWEVER...
the absolute BEST of all is L'ART DU SON. It not only cleans the CDS, it also provides a very natural sonic balance and almost seems to enrich the midrange. I use it on every new disc I buy. VERY highly recommended!