Users move between phones, laptops, and tablets. Stitching these sessions together is the biggest challenge in modern tracking. You must bridge the gap between anonymous visitors and identified users.

Deterministic vs Probabilistic

Deterministic matching uses a hard ID like an email or login token. Probabilistic uses patterns like IP, device type, and browser finger-printing (which is becoming harder due to privacy laws).

• Always prioritize Deterministic matching for accuracy
• Use 'Alias' methods to link anonymous_id to user_id upon login
• Ensure data is hashed and salted to maintain GDPR/CCPA compliance