If you buy a car outright for £10,000 and sell it 3 years later for £7000 it's depreciated by £3000. If you PCP the same car interest free and pay £1000 upfront and then £55 per month for 36 months with £7000 baloon payment you've still lost £3000, and you've still had the use of the car, it's just you lost the money over 3 years instead of on day 1 when you first bought the car. Plus, you have £7000 in cash tied up in a depreciating asset. Every accountant in the world will tell you that's a carp idea. In reality there are interest charges on a PCP so maybe it costs you £200 in interest, but that's a relatively small price to pay for the use of the car and the flexibility of the arrangement.
Finance isn't a bad thing, so long as you know what it's costing you. Very expensive finance is a bad thing though.