Hi there, power-off is not what you want either.
If you are upgrading software, the 'request system reboot' is your friend. 'request system halt' will halt the operating system, ready for the device to be powered down. I've not entered 'request system power-off' into a device for at least five years, however I don't recall that it did anything different over a halt.
When I upgrade Junos, I always reboot the node; then once it is back, I enter the following command to ensure that both partitions are running the same version of code - this is handy, especially if you are using features that are reliant upon a certion version of code.
request system snapshot slice alternate
In the event of an ungraceful powering down, the primary image may become corrupted and if the backup code is a different release, you can end up with missing configuration elements etc. This is also worth noting on the EX if you have a virtual chassis, as all members need to run the same version of code. You can check whether this is the case by entering the following command:
user@node> show system snapshot media internal
Information for snapshot on internal (/dev/ad0s1a) (backup)
Creation date: Feb 17 09:22:50 2014
JUNOS version on snapshot:
junos : 12.1X44-D26.2-domestic
Information for snapshot on internal (/dev/ad0s2a) (primary)
Creation date: Dec 13 19:03:38 2013
JUNOS version on snapshot:
junos : 12.1X44-D26.2-domestic
I hope this is of help