Bonding straps in load centers

I just finished installing a 'spa box', which is a 120 amp load center with a 60 amp gfci preinstalled. I ran 6/3 + ground. The box had an isolated neutral bar and a 'bonding strap' that can be used to tie the neutral bar to the box. The instructions weren't entirely clear to me, but I gathered that it was not appropriate for me to use the bonding strap my application. Is this correct?

In what case does one use the bonding strap?

In a subpanel, the neutral bus bar should not be bonded to the panel box, and there should be no connections between neutral and earth ground conductors.
 
The bonding strap is only used in a service entrance panel.

:hesaid:

That makes sense; I guess I just never contemplated someone would use one of these dinky little boxes as a service entrance panel.