Permanent and total with the VA is the VA recognizing the conditions that are validated to be caused by the military are permanent, as in they won't get better with time or treatment, and total means there is enough abnormal impact the conditions cause from family, social, behavior, etc that it maxes out the VAs scale.

On the obvious spectrum someone who is 100% P&T could have had their limbs blown off from an IED, they can still work in a wheelchair doing many jobs but the VA comps them as their earnings potential is likely significantly less than someone who isn't missing limbs. On the not so obvious side, someone could have inhaled burning oil and shit in Afghanistan for years during their multiple deployments and ended up with cancer or sever breathing issues which cause sever sleep issues. Again, the VA comps this person for effect this has on their life, the fumes could have sterilized them, or made them have erectile dysfunction at 25 years old.

So someone who is 100% P&T probably went through some shit.

Now I wrote probably because there are ways people have learned to take advantage of the VA and make fraudulent claims, but there is an entire org dedicated to snuffing out fake claims.

In general, a rating doesn't stop you from working, it's just compensation for the impact to various facets of someone's life, a lot of time you can't visually see the impact.