什么是Consent banner？
The popup asking visitors to accept or reject cookies and tracking, required in the EU before non-essential identifiers are stored.
A consent banner is the popup asking visitors to accept or reject cookies and tracking before a site stores anything non-essential on their device. In the EU and UK it is not decoration: ePrivacy rules require consent before storing or reading identifiers that are not strictly necessary, and GDPR sets the bar for what valid consent means, freely given, specific, informed, and as easy to refuse as to accept.
For measurement, banners are quietly expensive. A large share of visitors reject the prompt or leave before answering, so cookie-based analytics loses 30 to 60 percent of real traffic, and the missing visitors are not a random sample, which skews channel and conversion numbers in ways you cannot correct for. Dark patterns that make "reject" harder than "accept" draw regulatory fines, and "accept all" rates keep falling as browsers and users get stricter.
Whether you need one depends on what you run. Analytics can go bannerless by going cookieless; ad retargeting and cross-site tracking genuinely require consent, and a banner is the honest way to ask, as the GDPR analytics guide explains.