Private leases are for small businesses / self employed who get tax benefits and require a business use vehicle or for those who have a car allowance from work. Or need a car / van for a short period only say 6 months. Short term can cost a lot more and some rental companies offer better long term corporate / commercial rental rates.
When you lease, your entire payment each month is depreciation since you don’t own the car. However it is all relative as in this instance you don’t want to own the car which is the full benefit of leasing.
Don’t necessarily confuse leasing with contract hire / PCP type schemes from a main dealer etc which although in essence are the same things are a product sold to everyone and not necessarily those who need for business use. Notably though, these lease schemes can be much better value than using contract hire companies.
However the point of leasing when you get a car allowance is that you match you car allowance with the lease fee. Since the car allowance is just that there is no depreciation to you but to your company.
In my instance I get my basic salary which my pension contributions, bonus, future bay increases are based on. Then I get the choice of a company car or car allowance on top which is set at a value above the Benefit In Kind rate of the cars available at the employees grade.
Now to buy a car with the car allowance isn’t such a great deal since a decent car on lease hire with servicing etc included would cost me much more than the value of my car allowance.
Example, a Saab 9-3 180 vector td is on my company car list. I could take and not get my car allowance but insurance, servicing etc is paid for. However to buy this car on a serviced lease would cost me ~ £200 more than my car allowance pm with a mileage restriction of 10-15k per year. Alternatively, I can go to a Saab dealer and pay 1-2k deposit and PCP for ~ £300pm. Still not better than taking it as a company car apart from the fact I have a higher salary on my pay slips due to the car allowance.
Now contractually, I have to have a car for business. Since I already have a car, fully paid for and owned by me, it makes sense for me to take the car allowance and use this as salary top up to run the car, pay petrol etc.