I seem to recall that Phil Harris might have mentioned that more stress is placed on the harddisk during start up compared to leaving the device constantly on. This would be consistent with the following advice from Naim's Knowledge Base :
UnitiServe
Switching off the Naim UnitiServe from its rear panel power switch is not normally necessary unless it is being un-installed, so you can leave it on all the time. It can be put into shutdown mode by touching the front panel logo for five seconds.
The UnitiServe may take up to one minute to enter shutdown mode during which time the shutdown button will flash. The shutdown button will remain lit when the UnitiServe is in shutdown mode. Wait until the shutdown mode stops flashing and remains lit before switching off the UnitiServe from the rear panel mains switch.
Never switch off the UnitiServe from the rear panel power switch or unplug it from the mains supply unless it is in shutdown mode.
http://www.netserverapps.com/naimaudio/users/main.php?id=10120&category_id=16
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