I am with BT and have a good line from the cab and have lost about 10mbps due to the fact that DLM in the cab does not allow the modem to be off.
I lost 5mbps due to a power cut and during the bad weather I had extensive water damage , and the power had to be off again losing me another 5mbps.
BTW I use a separate modem and router.
What good is the DLM if there is no line faults.?
It can be handy for the ISP or OR to make some more money though I guess.