The button "Subscribe/Unsubscribe from Timer Service" does not clearly 
explain the fact that it determines whether or not Alarms are enabled in
ERP5. It is very counter-intuitive to see Alarms on "enabled" in the 
"Configure Alarms" screen and yet not have them being run because the
Alarm Node is not subscribed to the Timer Service.

/reviewed-on nexedi/erp5!539