What is a casita? A small separate living space on the same lot, usually detached, with its own entrance.
In the Southwest a casita is a small second dwelling on the same parcel as the main house: often detached, usually with its own entrance, and normally with a bathroom and some kind of kitchen or kitchenette. Elsewhere the same thing is called an accessory dwelling unit, a guest house, a granny flat or an in-law suite, and in Las Vegas listings some builders use casita for an attached bedroom suite that opens onto the courtyard rather than into the house.
The distinction that decides what it is worth is permitting. A permitted, separately habitable unit appears on the county building record, can usually be rented under local rules, and is valued as living space. A converted garage or a room somebody added without permits is a liability at resale and can be an insurance problem, and neither the listing photographs nor the word casita tells you which one you are looking at.
Kouzr reads the casita off the Clark County assessor's building record rather than off the listing text, because the county answers it for nearly every parcel in the valley and a listing answers it only when the agent thought to mention it. What the county cannot tell you is whether the kitchen is legal, so the permit history is still the thing to ask for.
A worked example
A 1998 Las Vegas house lists at $525,000 with a detached casita. The assessor's building record shows a 420 square foot casita on the parcel, which is why it appears on Kouzr's casita page; the permit history at the county is what says whether the kitchen in it was ever legal.
Las Vegas homes with a casita on the county record
Questions people ask
Can you rent out a casita?
Sometimes. It depends on whether the unit is permitted as a dwelling, on local rules about accessory dwelling units and short-term rentals, and on the HOA's own restrictions. All three have to allow it, and the listing is not evidence about any of them.
Does a casita add value?
A permitted one usually does, both as living space and as the reason a multi-generational buyer chooses the house. An unpermitted conversion often subtracts value, because the next buyer's lender and insurer both see it.