The verification process has two main purposes which are:
to ensure and demonstrate that all ballot papers issued at polling stations and all returned postal ballot papers have been brought to the count, and
to provide the figure with which the count outcome must reconcile
You should keep both of these purposes in mind when conducting the verification process.
Ensuring accuracy at the verification stage is crucial to ensuring a timely count. If the verification figures are wrong there will be a variance against the count figures which will need to be resolved and which risks significantly slowing the overall process.