The version 1.0 of zkSync protocol is using the PLONK proof system which requires a "trusted setup" of a Common Reference String (CRS). In PLONK, this setup can be done once and be reused by any number of applications (this is called Universal CRS).
Another big advantage of a universal CRS is that updates and bugfixes do not require their own trusted setup ceremonies (which are very difficult from the logistical and security perspectives).