I just bought a new Passport acoustic, and it has an extra saddle.

I think it's really nice of them to throw in an extra saddle, but in why would I use it? Will it allow me to use heavier gauge strings? What's the deal with the extra saddle? Also, what gauge strings come stock on these passports? 

thanks in advance

Hello AGTG, it is because some people like a non-standard saddle.  Lets say you like a lower action then you can modify away and have a backup if you go a bit too low.  

As for heavier strings I guess what you are saying is you could modify one bridge to accept the heavier strings at exactly the same action height as say very light strings on the other bridge?