We often fly our drones inside. This is not to say it's easy or automated, it depends on the circumstances and we take each flight on a case by case scenario.
What are some of the issues?
When you're flying inside with a lot of drones GPS can be an issue, or more to the point, lack of GPS can be an issue.
Most (not all) drones use GPS to pinpoint their position in 3 dimensional space. This is usually fine outside with good strong signals coming from satellites, however when you're inside a building or structure these GPS signals get weak or are blocked completely. This means you're flying inside with either just the vision positioning system or just in ATTI mode (for DJI users). Now the vision positioning system isn't fool proof, if you're flying in poor or low light the positioning cameras cannot always make sense of your environment, so ATTI mode is completely manual with no assisted flying and you really have to have your wits about you and have practiced flying in ATTI mode before flying in a confined space.
What about obstacle avoidance?
So a lot of the DJI drones have a system called "obstacle avoidance", wow, this is great you'd think, perfect. But in reality, when flying indoors, this is a hindrance.
I have crashed a drone inside before now because I had obstacle avoidance switched on. It had worked out that there was an obstacle in front of it (I think warehouse racking), then either decided to brake but at the same time it worked out there was a wall behind it and another obstacle to the left and right and a second later it was on the floor because it had hit something with very little input from me on the controls.
What it also means is you can't get particularly close to things, which when you're flying inside is inevitable. You are regularly flying within 1m of an obstacle, so I normally switch obstacle avoidance off, I know, counter intuitive, right?