Sync speed history for your broadband connection is captured in RADIUS and useful for noticing trends over time.
It's perfectly normal for your sync speed to fluctuate on ADSL/FTTC/SoGEA connections, so don't be concerned if you see a fluctuation in speed by a few Mbps. If however you see a drop from say 70Mbps -> 45Mbps, this could be indicative of a fault and worthy of further investigation.
Session History
Session history is similar to sync history, except it shows when your router connected/disconnected and why it disconnected.
It's normal to see disconnections occasionally, especially if they relate to maintenance (either by us or the carrier). Though if you see a large number of disconnections in a short space of time with reasons like 'NAS-Error', then this might be indicative of a fault and is worthy of further investigation.