How does cookie consent affect our marketing tracking?
Consent choices decide what you can measure. Consent mode recovers some of the lost signal.
A consent banner decides which of your tags are allowed to store cookies and send data, so every "reject" is a visit you cannot measure directly. Google consent mode softens that by letting tags adjust their behavior instead of simply not firing.
What a banner actually controls
Google's consent mode documentation defines four signals that a banner sets: ad_storage, which enables advertising cookies and device identifiers, analytics_storage, which enables analytics cookies, ad_user_data, which permits sending user data to Google for advertising, and ad_personalization, which permits personalized advertising. Your banner sets those four values and your tags read them. That is the whole mechanism.
Basic versus advanced consent mode
Google draws a clear line between the two. In basic mode, Google tags do not execute at all until the visitor interacts with the banner, so nothing reaches Google beforehand and conversion modeling has to rely on general patterns. In advanced mode, tags load immediately with consent defaulted to denied and send measurements without cookies while they wait, which lets Google build an advertiser specific model. Google also notes that modeling requires meeting a data collection threshold, which matters: a small account may not generate enough volume to get modeled conversions back at all.
The honest tradeoff
You get a better compliance posture and you lose observed data. Some of what you lose comes back as modeled data, which is an estimate, not a record of a person. That changes how you read reports. Modeled conversions are fine for judging whether a campaign is working. They are not fine as a bill of sale, and you should not reconcile them line by line against your CRM.
If you market into the EU, the UK, or a US state with its own privacy law, this is not optional. Put the banner up, wire consent mode properly, and keep your privacy policy honest about what you collect.
What to do about the gap
Lean harder on data you own. First party form data, a CRM that records source at creation, and offline conversions pushed back to the ad platforms are all unaffected by a cookie choice. That is where our analytics work puts the effort, because it is the part that keeps working as browsers keep tightening.
Related: What is server-side tracking and does our business need it?, What is offline conversion tracking and why does it matter for lead generation?, Is HubSpot HIPAA compliant for healthcare businesses?