Technically, there is not a tremendous amount of money lost due to his unused mileage, rather just depreciation of the vehicle solely based on age which would happen to a new car that was purchased or leased. Actual mileage (outside of the extremes) has a minor impact on the overall resell value and think we put too much emphasis on leftover miles especially since most cars are underwater when they are turned in anyway. KBB estimates about $1,800 difference for his car with 15K vs. 36K miles so $50/month.
Leasing vs. buying is always a personal preference and no right or wrong answer. The example you provided is a 5 year old car with 35K so like comparing apples to oranges. It’s two years older than the car he has today that is about to be turned in. Also, maybe he just enjoys having a new car with the latest bells and whistles.
The right comparison would be buying the same car outright vs. leasing and don’t think he would be in a significantly better position after 3 years owning the car vs leasing even if he only had 15K on it and signed a 30K lease. He would have paid the entire tax bill and still have to resell it and the hassle that comes with that. If he planned on running it into the ground, that’s a different story.
@jy1022 - Some manufacturers do 7,500 miles/year leases like Acura & Audi (BMW does not), but it’s not going to save you a ton as it’s typically just a 1% increase to residual ($500-$600 total over 3 years) vs. a 10K lease. If you like your BMW, I suggest you stick with them and focus on best possible deal you can get, potential a loaner as suggested or lower end model. If you follow this board and/or hire a broker, you can probably get a better deal than you would have done on your own which can easily offset the “wasted” mileage. If you are patient and have flexibility on colors/options maybe you can run into a unicorn deal like this and then the mileage is irrelevant: