hi hake - welcome to the forum
There does seem to be varying reports on this, and I can see both sides.
From experience it would seem that if you know which date you are going to be MAXed, then you are best leaving your router off that particular night if possible, so that the first time you sync up on max the DLM has the best chance of setting your bRAS profile correctly.
The problems is that everyones line is different and has such variations that I dont think there is a set rule that can apply to everyone all of the time.
My own thoughts are if you sync up at the max speed for your line and you are stable then you are probably best staying connected for as long as possible.
SNR can and does vary throughout the day, therefore if you resync in the evening there is more of a chance that you
may sync at a lower speed.
It is possible that you may sync at a lower than expected speed, therefore trying a resync in say the early hours or the morning, may mean that you do get a higher sync speed, therefore under these circumstances a reboot could prove beneficial.
I dont recommend doing lots of reboots since too many disconnections can sometimes fool the DLM into thinking you have been unable to maintain sync, and therefore you could end up with lower speeds.
IMHO, if you sync at a high speed that you are happy with, then dont touch it.
If you think you may get a higher speed, as outlined above then theres no harm in trying.
mr_chris could be testiment to the *if it aint broke dont fix it* rules. He had a steady 8Mb connection for 4 months.
After moving a few things around and a couple of resyncs, he found 2Mb lopped off his sync speed and interleaving being applied. So he was stuck with a 6Mb profile for 4 days.
During this time to get his speeds back up to 8Mb he had to do a few very carefully timed resyncs.
Therefore there isnt really a hard and fast rule.
Aside from if it works ok and youre happy - then leave alone.
I believe the information on the Plusnet site is taken from the advice in the BT video that soms mentioned.
The link to the video in this thread:-
http://forum.kitz.co.uk/index.php?topic=83.0