EX4600 Junos Upgrade ?

We have been using EX4500 and EX4200 switches for several years. To upgrade Junos on these switches we have been:

1. Using WinSCP to copy the .tgz file into /var/tmp
2. Issuing this command
   request system software add /var/tmp/<NameOfPackage.tgz>
3. Then this command
   request system reboot all-members

We have a new EX4600 in production and after a bit of research it seems like I should add the force-host as shown below

request system software add /var/tmp/<NameOfPackage.tgz> force-host

Should I be adding the force-host at the end?

What exactly does the force-host do?