Cert of Practical Completion means that the works is in effect complete. It is not necessary for snags to have been completed for the Cert to be issued.
In many cases, it means that the client can take possession of the building and has beneficial use of the building. The idea is that snags would be dealt with later. The onus to insure the building passes from the builder to the client within a number of days of the Cert being issued.
Does this then trigger the final payment to the builder?
If something needs to be re-done because of poor workmanship, does this fall within the definition of a "snag"?