unplug the phone line in case of lightning.
Sadly, I didn't when I was away from home last week. Came back to find that interleaving had kicked in during a thunderstorm and max attainable downstream speed had dropped by 12Mbps - fortunately, I still have an 80/20 connection (downstream INP of 3 and drop in SNR). My error rate is very low though so there are some pluses.
seconds with Remediable Errors (FEC) Unrecoverable errors (CRC)
Errors (ES) many
Errors (SES) per
15 minutes per
FRITZ!Box 1 0 20 6 0 0
DSL Telephone Switch 11 8 0.56 0 0 0
Now the wait (usually weeks for DLM) to do its thing