This post should help. As it explains, you need to carefully consider the consequences of that option.
Even if you do opt to have people records added automatically, they will only show information that already exists in the database. To get a full filmography and other data, you still have to import. So it's kind of a no-win situation. If you automatically add people, you'll then need to update many thousands of records, most of which you don't care about.
What I'd dearly like to see is the option to have people records automatically updated—if and when they're selected from the Movie view. That way, any new link selected would result in the target record being updated within a few seconds. The same thing could be done for existing records that haven't been updated within x days. That would ensure the data viewed for existing records isn't stale.
We would still have the ability to mass-update all people or some reasonable subset of them, but that's just not practical to do on any regular basis—for a large database. With such an option, I'm sure I could happily use my database for six months to a year, then mass-update all records (for people still living) that haven't been updated during that period.
