If you can "manually" lock and unlock the rear diff (some europe models have a rear diff that you can lock/unlock due to ceratin rules for some registrations forms) those that has the manual lock has an extra switch for locking the rear diff.
If it has a rear diff as most atv it alwais gives both rear wheels 50/50 power going in the diff. It's not a real differential realy because it made so that it always gives the same amount of power to both wheels. (don't know a better explenation of it in English) Here in europe the c force 800xc/850xc and c force 1000 has some kind of atomatic rear locking differential.
It's not harmful to drive on roads with it. It will wear tires a bit faster then a viechle that has an open rear diff.
I have a cf moto c force 520 (500s for the us market) and almoust got 30000 km on it and over 1000h on it and a lot of those km is from road driving. Haven't had any rear diff problem yet exept i had to replace the diff seals once.