Just think about all the things that a CBC and blood panel show. It's not worth skipping.
Blood cells. Platelet count. Infection?
Liver and kidney values. Organ function?
Electrolyes?
Etc., etc., etc...
A lot of times it is skipped for young dogs, but the problem with that is young dogs still have organ dysfunction and they can get infections, etc. IMO, for an elective surgery it should absolutely be done and spaying is elective in most cases. They wouldn't skip it in human medicine.
