Oh, then I'd say yes, better safe than sorry! For example, my house has had the occasional mouse run through, and mice can have fleas and worms which can be passed on to the cats, so I always will have their stool tested for worms.
Yes, it's done every year for indoor cats. A parasite could be tracked onto the carpet or in on someone's clothing. Better safe than sorry.
As for what it is...
You bring in a recent piece of the cat's poo. I use a yogurt container to carry it. The vet floats a piece of this in water and watches for escaping worms. Nasty but necessary.