What is the meaning of this Option of vCO:-
Number of Menu Operations and their Workflows
while installing the vCO workflows in vCAC
This is to maintain a version for the vCAC workflows that are run. If you don't put it, it'll be 0.0. Usually this starts from 1.0.
as per one of blog post it's written it's not needed anymore with vCAC but this is just version of Menu only then why it's not needed anymore?
Yes from 6.0 it's not needed. I think the numbering is taken care of.