From random movement to maps
The first Roombas drove around at random and bounced off obstacles. Even so, within an hour they had cleaned most of the flat. Newer models use a laser scanner (LiDAR) to build a map, divide it into rooms and clean in systematic lanes.
Privacy
A robot vacuum with a camera and a map of your home is an internet-connected device. Manufacturers should protect the data, but there have been cases where photos from inside people's homes leaked. When choosing one, it is worth checking whether the vacuum can also work locally, for example through Home Assistant.