I remember that time when for the tracking you had to just set up Google Analytics, configure goals, and you are set. Those were the times! Nowadays the tracking setup is a complicated task from a technical standpoint.
Let's highlight the main challenges, consequences, and possible solutions.
Consent mode
Due to Data Privacy Regulations consent should be granted before tracking cookies could be used. From my observation, the majority of projects simply don't activate tracking prior to the consent, which is actually a mistake. Why? First of all, the acceptance rate of the consent could be lower than 50%. Secondly - Google Analytics could be activated in cookie-less mode, therefore data could be collected even if consent is denied. The setup could be enhanced with link-pass-thru functionalities - which add tracking IDs to all links on your website.
Browsers built-in tracking protection and Decreased Accessibility of Third-Party cookies.
Sounds too complicated, in other words, it means JS trackers can't set their cookies and in some cases (thanks to Firefox) - they are just blocked. What can we do to bypass the limitation? Use Google Server Tag with your (sub)domain - it unlocks you once again to use cookies as well as bypass tracking blockage.
Why is it important?
The aforementioned issues complicate conversion attribution to sources, which means - your Google Ad campaign gets fewer conversions, fewer conversions -> higher costs -> more expensive leads.
From my experience, proper tracking implementation can give you 10-25% growth in lead attribution to channels.
Another challenge that I noticed multiple times: was miscommunication between departments. The marketing team doesn't know technical details and it is hard for them to describe the task as well as verify the tracking. For the developers - they are not familiar with analytics and it is boring for them to dive into that, which leads to mediocre implementation.
Proper tracking implementation and verification are the first tasks before campaigns.