What are the legitimate applications for entering dreams in Inception?

In Inception, Cobb and his team use their talents to extract information from people's minds by entering their dreams. This is generally used for corporate espionage and is considered illegal.

However, Cobb mentions to his father-in-law that after the death of his wife, he could no longer use his talents legitimately, which makes me wonder what the other in-universe applications of this are.

Aside from a brief mention of military training as well as training clients to withstand extraction, are there any other legitimate applications for entering dreams, either explained in ancillary material or by the filmmakers?

There are a range of legitimate potential uses for the PASIV machine (and lucid dreaming in general) seen within the wider Inception universe, starting with those you've already mentioned;

To prevent people from performing extraction on you.

ARTHUR: Fischer's had an extractor teach his mind to defend itself. His subconscious is militarized. It should've shown on the research

Inception - Script

Military training.

ARTHUR: That's why the military developed dream sharing-a training program where soldiers could strangle, stab and shoot each other, then wake up.

ARIADNE: How did architects get involved?

COBB: Someone had to design the dreams.

We should note that Cobb and Mal seem to be paid to engage in 'Dream research'

COBB: We were on a job. Exploring dreams within dreams. But we didn't understand how your mind can turn hours into years. How you can get trapped. Trapped so deep that when you wash up on the shore of your subconscious...

Inception - Script

Cobb and Mal were originally introduced to dream-sharing by Stephen Miles, a senior professor at the École d'Architecture in Paris. The military presumably approached him to locate real-world architects to design their training simulations and he in turn recruited Cobb and Mal to work with his clients. According to the opening of Inception: The Cobol Job, he saw the dream-share as presenting an opportunity to design structures that can't exist in the real world.



"Professor Miles brought us into Dream-Share to prove to us our creativity knew no bounds. He was right. What God took six days to do, we could do in thirty seconds. While we rested...Professor Miles wouldn't have approved of this. Creation should be for the sake of creation. Not for profit."

Lucid dreaming is used as entertainment

ARTHUR: We got a problem. My tail just followed Saito to an underground dreamcade. Apparently, he’s a regular there.

NASH: Big deal.

ARTHUR: The big deal is now we know Saito’s familiar with the dream-share. If he’s been playing games inside it, he’s probably got command over the dream.

Inception: The Big Under

Note that Arthur highlights that Saito goes to an underground dream arcade, suggesting that there are others that are more vanilla.

The pseudo-documentary Chris Nolan Research Footage (an in-universe discussion of the principles of lucid dreaming) mentions a range of potential uses for the PASIV machine and 'Project Somnacin'.

To help those suffering from traumatic nightmares.

...we have techniques that can train someone to stay in the dream and with a practice one could stay in a dream for an extended period of time. Therapists have been using this skill to help patients with night terrors so when a patient's in a nightmare, they're trained first to acknowledge that they're in a dream and they can change the experience from a negative one to a positive one. It's incredibly powerful once the skill is mastered.

To train soldiers to be able to maximise the amount of REM sleep, hence making their sleep more restful.

[our] training regime is designed to resolve sleep disorders in the field when engaged in combat with the severity... the quality of sleep becomes extremely important. We train them to get good quality rest... discovered optimizing REM sleep increases one survival abilities That's because the brain during REM sleep is exposed to worst-case scenarios. The more REM sleep our soldiers get the more on their toes they will be.

Captain Darren Bartel - Project Somnacin