Why incinerate the entire room?

What they are trying to do is match the new session to the original session with Delos, and that's how they measure success. That means the condition of the room must be exactly like it was at the beginning of the original session. But we see Delos in there moving things around, consuming tea, scotch, etc. Any variation of the room in its beginning state could affect the rest of the session, and they wouldn't know for sure if it was the room or something wrong with Delos that caused the session to go differently. So they completely wipe the room and the machines are able to precisely recreate its contents it in a way that would be difficult for humans to do.

There is one exception- the humans he interacts with are always changing across different trials. Like William aging over time and the assistant who appears on the screen to tell him there is a visitor. This could be a clue as to why they cannot successfully recreate Delos.

I don't think the Delos corporation cares too much about laws. Especially privacy ones heh.

It still doesn't make sense to burn imo. Is it easier to to say, pick up a cushion and throw it in the bin then put a new one in it's place. Or cremate it in situ and clean up the mess then replace? Scale that up to beds and stuff, just unnecessary hassle.

Removing everything seems more efficient that cleaning up after a fire.

I just don't buy it. They don't need to incinerate all that inside the room. They could remove it and then burn it somewhere more convenient.

Assume each attempt lasted about a month - they started out shorter and ended up longer, so take one month as an average. 30 years = 360 months. 360/149 ~ 2.4, which means about nine or ten weeks (2.4 months) total for each trial. In other words roughly five weeks after the termination of one experiment to analyze the data gathered and prepare for the start of the next. 149 attempts gives you a pretty rigorous schedule throughout those thirty years. They were going nonstop!

OK. That is possible. Does still seem a bit over the top when they could just strip the room instead.

No, the whole point was to establish a functional connection between the mind and its new body. What they found after many iterations was that his inability to adapt to his circumstances was the real problem. Not the mind-body interface which should've been working.

Notice how his condition deteriorated sharply after each conversation with William. The tremors were pretty much gone in that final attempt but as soon as William came in and told him a bunch of things about events since his death which upset him, he started to glitch. The hardware was fine. The weak mind inside was the issue. When William said they could probably figure out how to create a viable version of him, I take it he meant altering parts of his consciousness until they got something that was stable - i.e. the new James Delos would be a somewhat different person than before. But William had come around to the belief that his father-in-law (in any form) was not a man worth saving.