Isolated devices are the devices which have their substrates isolated from the rest of the circuit. This comes in handy usually when you need to use S-B connection in NMOS devices, but if you use this as a design methodology you can significantly reduce the substrate noise coupling from whatever digital circuit you have on the outside. Some processes offer triple well which makes it even easier to separate the sensitive devices from others.
Disadvantage is the area. You'd expect performance to be different but it's not in line with claims and measurements, so somehow they give the same performance, I just accepted that as magic and I'm no longer questioning it.
Refer to your process documents and stuff for details, this is just my limited knowledge.