I have been a busy gal over on the frontier of OpenSim, and "no" this is not a bid to lure you away from the beauties of SL (but hopefully I will have a video soon that might have you rethinking that "OpenSim has no art" rumor). That's another day and another story.
This is about NPCs. Maybe we should simply call them clones because that is what they really are.
Get yourself duded up (and yes, if we are talking a male character that means "duded" in the real sense of the word). Rez a sphere, add a script and the animation(s) you want to use and click. You have an instant character with very little lag who can be a non-speaking actor in your own personal play.
No more worrying if your computer can handle an extra avatar or two. Simply plop your clones out (on your own sim in most cases of OpenSim or ones where you have rights) and click. Some are designed to go away when visitors are a certain distance away; some stay put; some act as greeters and hand out notecards.
There are some caveats of course, no scripts in your outfit (pretty easy in OS, not so easy in SL but the rules may be different there), don't delete the pose ball without first turning your character off, etc. I took a class and was happy that I did.
I am populating my OpenSim city with some pretty interesting characters, and yes, it IS a challenge because I can't just dig into my expansive inventory or do a little shopping at my favorite venues to find costumes. I am making the animations myself and of course some of the props.
And, to be fair, until you feel secure with your cloned actors, it can be a little scary. Once you understand the options in the script (not terribly hard as I can do it and scripting is definitely not my strong suit) it is mostly the animations and getting the look together.
THINK OF THE POSSIBILITIES.
I haven't researched this for Second Life, but I know we have bots and "models" and such so I am guessing the technology has been available for a long time. Maybe some of you have even used this method. But to me, it was a revolution in thinking.
Sometimes you need to leave the comfort of home to learn new things.