What are the advantages of CPW over microstrip?
Keep in mind that circuits are usually printed on double side full-metalized dielectric boards, so by using CPW technology :


You use one face of copper instead of two, which, in large scale production, is a non negligible saving on costs since you have to buy single-face metalized substrates instead of double.
You remove less copper when printing the circuit, because what would be removed on non coplanar microstrip is now a conductive ground plane. Which also lessen the tool fatigue if using mechanical engraving


Here is a good reference comparing the two technologies made by Rogers Corps, which is a company specialized in radiofrequency substrates (like RO3003, RO4003 ...). however they seem to focus a bit more on CBCPW (conductor backed coplanar waveguide, another variant)

Another one which is a simple table comparing the two from a functional point of view